Uh, Caldria, psions sword is in ToB.

What is so good about skeletal warriors, when i used them they didnt seem to do anything, are they immune to their intelligence drain and stuff then?

The BEST summon spell against Illithids/mindflayers is Mordenkenain's Sword. The sword is completely immune to all mindflayer psi attacks.

Send it into any mindflayer room BEFORE any of your fighters. The mindflayers and umber hulks will waste their initial psi blasts on the sword.

The potion of clarity or chaotic commans cleric spell are essential to protecting your fighters. Also the potion of genius (+4 INT) or the potion of mind focusing (+3 INT, +3 DEX) are very useful to counteract INT drains.

Don't bother sending in summoned elementals. One INT drain seems to be enough to kill them.

Keep non-pis protected characters well out of range of the mindflayers, at least until you have completely engaged the MF's and UH's in a good melee. Then you can sneak up your other characters to supply long range fire support.

Keep a close eye on your melee fighter INT. If it drops below 6-8, withdraw that fighter or drink another INT raising potion.

Mindflayer lairs are really quite managable using these solid tactics.

I will quote another boardie here, with regards to Skeleton Warriors and Mordenkenain's Swords. ;)
<blockquote>quote:</font><hr>
They have no brains, they have no brains.<hr></blockquote>
5 of any of each will be a force to reckon with against the Mind Flayers. Just remember to cast Death Spell to instant kill all the Umber Hulks.

... or just be fast. With my berserker, slap on the Boots of Speed, drink Oil of Speed (very good speed aftert that!), use Draw Holy Might (or whatever the special ability is) and charge heh. Target Illithids first. I went through the first Illithis place (with the Hammer of Thunderbolts) very fast. Gotta keep the eye on the INT though, I had 1 left when I killed the last one heheh.. Close call. There are potions which raise the INT, one raises INT and DEX. I suppose they should stack, so even better - get +7 to INT and +3 to DEX, and then charge the room :D

And, there is no resistance against it as such. What I don't know, have not tried, is whether the Restoration, or Lesser Restoration, would restore the INT. In a way, it's drain like any other there is. Maybe it works and could help, though you would need to rest after the battle, since restoration drains the juices..

The standard cheese way to beat them is to use a cloudkill wand (NOT the Cloudkill spell) if you have one. Open the door, cast, close the door. The super-intelligent mind flayers can't seem to open the doors of their own lair. Like I said, it's a Camembert solution. :D