[Olorin]

Try various combos of fire/cold resistant equipment.

Fire Resistant Items(Highlight for %Resistance):
20% Mage robes of fire resistance
50% Red Dragon Scale
15% Aeger's Hide (Leather)
20% Darkmail (Chain)
20% Helm of Defense
25% Dragon Helm
25% Dragon Scale Shield
40% Ring of Fire Resistance
50% Ring of Fire Control
50% Taragarth (Bastard Sword)

Cold Resistant Items
20% Mage Robes of Cold Resistance
15% Aeger's Hide (Leather)
20% Helm of Defense
25% Dragon Helm
25% Dragon Scale Shield
50% Boots of the North

Level 3 Cleric or Mage spell Protection from Fire is useful until you have enough items (then learn more fireballs!)

Also, I have heard that the spell Sunfire sets your fire resistance to 100% for a short duration (I think that's how your mage is unaffected by it). Don't know how long that lasts since my cleric/mage was using items anyway.

I would recommend pumping your immunity to fire
a) more enemies cast fire spells than ice ones
b) your own fire spells are more useful since they don't risk destroying items

An annoying effect (or bug) that I found was that if I had my party lob extra fireballs into the melee (since I was immune), they still interupted my castings and made me say "ugh" in pain. So don't be surprised if Imoen's fireball causes you to mess up your casting of sunfire.

Just imagine the carnage if you had over 100% fire resistance and your party was casting various fireballs, firestorms, incendiary clouds, etc. at you and a mess of enemies. You'll be effectively regenerating while they turn into charcoal.