My 3 main fighter types - a dwarf fighter, a human ranger, and a human cleric) are all 5th level. My other three chars - a human thief, a half elf cleric/mage, and a half-elf fighter/cleric, are 5th, 3/4, and 4/4 (i think). Anyway, my party gets used as a chew toy by the Verbeeg. I managed to take out the acolyte and the first two Verbeeg, but the next two killed all but the cleric/mage and the fighter/mage (who were standing well back). I used missile weapons as much as possible with the cleric, the thief, cleric/mage, and fighter/cleric, while the ranger and the dwarf blocked the hall while fighting the verbeeg. My dwarf has 71HP and was the first to go down, while the ranger has 54 and was the second to go. Needless to say it got messier from there. I made it out with those last two, but left everyone's stuff behind (I planned on restoring from a saved game anyway). Is my party too underpowered to handle giants? or did I just encounter a long run of bad luck? If I am underpowered, what levels should I attain first, and where do I get the experience? It seems to me that there are few random encounters as the maps are not the same as in Baldur's Gate, where you could wander around and get random encounters.

You are fine. Just use LOTS of Stinking Clouds, Web and Entangle spells. Since your mage is only 4th lvl I would also suggest buying a few potions of speed for your artillery. All in all, just be patient and plan ahead!
Bueno Suerte...

The Veeberg level is very tough because they have huge to hit bonuses based on their strength (20-21 maybe?) The way I did it was have everyone keeping everyone at a distance and then meleeing only when they are about to be finished off. You can always outrun them and I recommend you do so.

What are THACO and AC of your characters?
Contrary, I have found this dungeon easy,
I made it without having to rest. I have
2 Fighters, Ranger/Cleric and Fighter/Mage,
I believe fighters were 5th level,
Ranger/Cleric 4/4 and Fighter/Mage 4/3.
All have AC between 0 and -3 and THACO
around 10-13. if you came there with worse stats you can try to summon some creatures
(or animate undead) so you can shot at enemies at distance.

Thanks for all the hints. I finally made it through with only my dwarf fighter joining the proverbial choir invisible. Web didn't have much effect on the Verbeeg, but having my clerics set up glyphs of warding down the hallways and having one of my fighters lure the verbeeg down the halls, helped soften them up enough for the rest of the party to pummel them with missile weapons and magic missiles. Whew. Tough, but I made it through.