Ok, I've been killed by him for about 20 times, and I'm reeeeaaaally tired of it...so can anyone please tell me how I can kill him?
I've tried everything.

What kinda characters are you using to fight Torgal? You can cast haste on your strongest fighter and cast Sanctuary on a cleric. Load up your fighter with the best AC items and the best weapons that you have. Try to make sure he/she has a lot of healing potions and ready your cleric if possible. If you can bring in any help (summoning spells for cleric or mage) cast them before you enter. If you have any stoneskins, that would help too. You can weaken him by just walking in the doorway and cast fireball before he initiates conversation. Try to take him out first, cause he is the toughest. Also, if you have a thief, have them use stealth and try to backstab him while the others fight. If things get too bad (AFTER you kill Torgal), retreat back through the door and close it. Then you can rest up until you are ready to fight the other two. If it looks pretty good after Torgal goes down, then finish them up. Remember to burn the remains and you are ok.

All of what I said are some general rules, but it really all depends on your party. If you have a higher level group, then you have many more options available.

An easy way to beat Torgal is to send an invisible character in. Torgal can sense invisible characters, so he'll initiate conversation and then run off after you. Draw him back into the previous room and ambush him for an easy kill. The other two trolls are actually harder variants of most giant trolls, but they're pretty lightweight next to Torgal himself.

I tried doing it that way before, but during the time it took for him to get in the door, I couldn't close it and the other trolls were able to get in. It's an easy fight if you can get him alone though.

Here is an easy tactic for those that have Yoshimo in their party.

Have Yoshimo set every one of his traps at the bottom of the steps just inside Torgal's room.

Have your party completely buffed up with all the protection spells, haste, etc. Make certain that you have some sort of fire or acid magic or arrows ready to finish off any troll once it goes down. Every arrow you fire at a troll need not be a fire arrow. Only the LAST one.

Have your fighters close enough to the door to bottle them up in the doorway and prevent them from getting to your spell casters.

Send in one of your characters in to get the troll's attention, BUT avoid the traps (i.e. walk around them). Once Torgal and his 2 pals start chasing you, run back to the rest of your party, once again avoiding the traps. Torgal, et.al. will run right over the traps and take considerable damage.

Now kick some green troll butt!!!

I thought you could walk over the traps? Thought only enemy would trigger the traps. I didn't use a bounty hunter to set traps though, I used a pure thief. Is this the special traps that a bounty hunter gets. Tell me man, inquiring minds wanna know. Yoshimo died early on in my game, so I didn't get to use him that much.

Yes, only hostiles will be affected by a snare, just like the horrid wilting spell.

Keyword here: Cloudkill. LOTS of cloudkill. Scoot a thief in their [very slowly as the thing initiates conversation] Line up some mages and shoot them simultaneously right to the edge of your sight [pause game to set them all up] BE SURE YOU SAVE JUST BEFORE!!! This will help if you need to reload so you'll have a better idea where to stop the theif [anybody will do really as stealth/invisable does no good here either...] -Cheers