There aren't shortcuts for converting between role-playing systems; a little legwork is required. However, Tunnels and Trolls is a particularly straightforward (and light-hearted) system, so it should be easy to see what is analogous in your system to the mechanics used in T&T.
T&T ostensibly uses D6 dice throughout, but as other polyhedrals are readily available these days, they will tend to crop up too, in scenarios at least.
Combat rounds are 2 minutes long, full turns 10 minutes. Wizards can only cast one spell per combat round, or 5 per turn. Expended strength (usually through spell-casting) returns at a rate of 1 point per turn, though the GM may forbid this if the character has been exerting him/herself through that turn..
There are warriors, wizards, rogues and warrior-wizards. The last two aren't much cop, and warrior-wizards are very unlikely to arise anyway due to the criteria for being one (all original attribute rolls 12 or above - likelihood: 1 in 360).
Warriors can use any weapon, assuming they have sufficient Strength and Dexterity, and get double protection from their armour.
Wizards can cast spells (expending Strength temporarily) but can't use (non-magical) weapons rated above 2 dice. (Basically they're stuck with daggers and sticks.) They can also detect magic within 30', sensing good or bad 'vibes' from it. A little quirk in the system is that the proximity of meteoric iron negates magic of levels 1-3; a wavy dagger called a kris is assumed to be made of this stuff and wizards do not carry them! Might as well give Superman kryptonite fillings. Wizards can use a magic staff to reduce the Strength cost of their spells; the deluxe version is sentient, learns spells itself, and can use its bearer as a battery for its own spell-casting agenda. Warriors are wary of plundering wizards' corpses...
Rogues struggle to cast spells and don't get the armour bonus. Warrior-wizards aren't much better. Most parties of dungeon delvers include a wizard, but the bulk of the party is usually warriors.
Characters can be human, dwarf, elf, hobbit, fairy (nobody bothers with these), leprechaun (gimme a break), or, "with the GM's consent", anything else. Attributes are adjusted accordingly. We tend to refer to them all as 'delvers', because they delve into dungeons, or something. Characters advance in levels by acquiring Adventure Points (APs), which are ladled out by the GM on the slightest pretext. 1000APs gets you to level 2, 3000 to level 3, 16 million to level 20 (I kid you not).
T&T characters have 6 main attributes:
Each of these is initially rolled on 3d6, thus varying between 3 and 18 and averaging 9-12. Different 'kindreds' have modifications to these attributes - dwarves, for instance, have doubled strength, elves one-and-a-half times as much charisma. Broadly, however, starting attributes will be less than 20 and will never exceed 36. A character is unconscious if ST or CON falls to 2 or 3, thereabouts. ST returns at a rate of 1 point per turn of non-strenuous activity (and wizards expend it through spell-casting), but CON returns only via magic or a rest of days or weeks. Characters with high CHR are natural leaders. (By convention, monsters have negative charisma, but this has no effect on game mechanics.) Weapons and armour have ST and DEX requirements, and spells have IQ and DEX requirements.
Adds derive from these attributes and give a bonus in combat: a character's Adds are calculated by adding anything over 12 on ST, LK and DEX, and subtracting anything under 9. Example: with ST=15, LK=4 and DEX=20, the character's Adds are +3, -5 and +8, for a total of 6. This 6 will be added to the character's total score in combat. Missile Adds are exactly the same, except that the bonus (or deficit) for DEX is counted twice, to reflect the importance of dexterity when using missile weapons.
Unlike many other systems, T&T cheerfully sacrifices realism for fun, and characters' attributes are likely to shoot up like crazy as they go through adventures. Characters receive a bonus to at least one attribute every time they go up a level, for instance. GMs will have to consider how such effects might best be construed in their system of choice. You'll think of something!
There is one other attribute, Speed (SP), which is always a simple 3d6. Not all GMs bother with it, and unlike the others it can't ever go up. But in T&T all rules are negotiable...
In T&T, saving rolls are used all the time to attempt anything whose success depends in large part on your attributes. A target figure must be reached by adding 2d6 to the relevant attribute. If you roll a double, you keep that score and roll again. Several doubles in a row can thus allow a character to achieve feats that would nomally be beyond him. The target figure is determined by the level of the saving roll. If the GM tells a player to make a level 1 roll on Luck ("L1SR on LK"), he must reach 20 by adding the dice roll to his LK. Level 2 is 25, level 3 30, and so on, up in 5's. Another way of figuring this out is (5 x level) + 15. Broadly speaking, only novice characters are likely to fail level 1 rolls, whereas a level 5 roll (40) might well be challenging even for a level 5 character! (There is no real connection between the two uses of the word 'level' here - it's terminology designed to confuse!)
A final rule on Saving Rolls (SR's) is that a player fails, regardless of his attribute, if his total dice score is less than 5. Given that doubles 'add and roll over', this can only be achieved 4 ways (1-2, 2-1, 1-3, 3-1) - so a player will fail to make a 'min. 5' about 1 time in 9.
Combat takes place in 2-minute rounds, in which a character may fight or cast a spell (which takes effect at the end), not both. Scores are achieved through a combination of dice and adds derived from the weapon(s), and 'personal' adds derived from the attributes (see above). The goodies and the baddies compare total scores and the higher score wins the round, the difference in the cores being the damage inflicted on the losers. (The score therefore incorporates the effects of parrying.) If a weapon is rated 3+4 and the character's adds are 12, he would roll 3d6 and add 4 and then 12.
Monsters may be described by a single number called the Monster Rating (MR). This is the damage it can take before dying, and its fighting prowess is derived from it too. Divide an MR by 10 (dropping the remainder) and add 1, and that's how many dice it rolls. Half its MR is the adds it receives. Hence a python with MR50 would get 6d6 + 25 in combat - but if it lost the round and took hits, its MR would be reduced and so too would its fighting prowess.
T&T weapons don't go above about 6d6 and a few adds, and you tend to need two hands for that. That's ordinary weapons, of course. With magic weapons, the sky's the limit.
Armour and shields are rated at so many 'hits'. A cheap buckler (round shield) takes 3 hits, so if the bad guy beats you by 5 points, only 2 would come off your CON. Warriors are deemed to be able to use their armour and shields more effectively, so their hits are doubled for these characters.
Characters speak their native tongue (Elven, Dwarvish, Orcish, etc.) and get to roll on a language table once for each point of IQ above 12. Half the time this will result in their knowing the Common Tongue, which is useful. As well as 'High Tongues' (spoken by us intellectual folk and dragons) and 'Low Tongues' (spoken by cows and other folk we tend to eat), there is Wizard Speech, which is a vaguely-defined telepathy comprehensible to all, but spoken by very few (and it needn't be wizards).
Updated 26/06/00 by Jason.