I just got to the underdark, and I've decided to use a walkthrough for sure. There was a gate with an air elemental and they kept coming and coming, so I killed them all and then I came upon a group of drow that wanted to destroy me and were tough. So, back to the auto save when I entered the region. Any general tips? Not necessarily spoilers though, thanks.

If your not ready, then build up your party some more. It is a tough area. There is a place to rest and restock, so find it early.
Mini-SPOILER
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Among other things, you will need to face Gauths, Beholders, Mind Flayers, Elementals and Drow. All tough. The drow part is resolved without much combat, mostly intrigue.

You don't need a walkthrough; there's only one or two groups of Drow that you need to fight in the main cavern and only one of them is very difficult. The one with the 6 or 7 Drow in a wedge formation is tough because there are many spell casters (mages and priests). Fight the easier group first and get their fantastic armor... :)

To fight the big groups it is best to use area of effect spells. Cloudkill and web cast together aswell as the occaisional fireball works surprisingly well.
Just take off the AI and give everyone apart from your tank a missile weapon.
Pound the Drow b***ers and anyone who emerges from the are of effect meets the tank.
SEND THOSE OVERGROWN PIXIES BACK TO HELL!!!

I wouldn't go to overboard with spells, they have a fairly high MR.

my 4 hasted berserkers were so happy they had something to slash up :D

the only thing that works decently on them is brute force!

Spoiler

About the portals, the elementals come from some other place through the portal again and again. You can stop it by killing them when not close to the portal (and not come back there again) or when free the Imprisoned Mage neer the Earth Elemental portal (with a freedom-spell, that can be bought from the duergar.)

And indeed you don't need a walkthrough, all quests with explanation are given here ;)