Drow Ambush Options

[Zarathustra]

Alright. I've done the Drow ambushes before, but I'll be damned if I can figure out how (other than blind luck). After doing well enough so far, I've been stuck at the first (the non-dispelling) Drow fight for three days now. I know Sikret will tune it down for next version, but for now, I'm stuck with what is. So, any and all non-cheesy tips will be very welcome, including the heaviest of spoilers.

Party:
NPC - Vagrant (FoA, Frostreaver)
Valygar (V's Katana or Club+3, Belm)
Minsc (Lilarcor or Spear of Impaling or Staff+3)
Sir Anomen (Ashideena or MoD)
Nalia
Imoen

Average XP is about 2,800,000; the Beholder and Illithid lairs have been cleared; lots of healing potions are available, but almost no other potions; haven't forged a single IA item yet. As I said, up to this point, the game has been of moderate difficulty - usually two or three reloads per improved encounter.

SPOILER!

The main tactics so far have been either (1) a summons-heavy full assault, or (2) a summons-heavy pincer movement followed by retreat, trying to separate Drow from spiders, or (3) a fire-based tactic (let's not talk about that one...). In every approach, my priority has been to take out the two Ghost Spiders ASAP, then mop up the other spiders, finally the Drow. Also in every approach, Imoen has been blasting away with Horrid Wilting and Emotion from the rear while a buffed Nalia tried to divert some attention from the frontliners. Basically, I can never take out the Ghost Spiders before being crippled by the Drow to such an extent that the Fallen Devas, Flamestrikes, and remaining Spiders then slaughter my party. I'd split my warriors into a first-phase and second-phase group - one to kill the Ghost Spiders and probably sacrifice itself, the other to hang back in order to later face the spellcasters with their crucial buffs intact - but even with two Swanmays, there's not enough melee power for that to be effective.

So, I'd appreciate advice. Thanks in advance!