Thanks all, for your tips. I didn't have any magical ammo left for missile weapons, so here's what I did:
As soon as the dialogue with the Undead Lt is over, cast web just in front of him, knowing that it'll snag most of the cold wights I *know* are sure to appear immediately.
Follow-up with a fireball or two, then send in my fighters (equipped with ring of free action) into the fray whilst cleric turns undead and bard plays a song. They can't do anything else anyway except waste ammo on the cold wights to no effect.
When the blast skeleton makes its appearance, pull back fighters whilst rest of party attack with ranged weapons. Usually works.
The poison zombies were pretty easy, the imbued wights were nasty due to their magic missile attacks. My paladin bore the brunt but managed to survive. Once the MMs were expended though, the imbued wights were pretty easy.
On to Level 4!
