I finished my first "playthrough" with a solo Dragon Disciple at insane difficulty. Against golems in OC, i tried everything. spells to lower his magick resistance, a lot of powerful spells, and even tried a "one time wish" to kill then(they took no damage). The solution was time stop + melee attack, then time stop again and melee attack(...), against the final boss, i have used a eqquipment to increase my character speed(since my defenses are dispelled) to let me take distance and used some spells, without Tenser's transformation, Time Stop and Black Blade of Disaster and meatshield summons to give some time, i probably will never be able to complete the game.
Spell resistance is IMHO a think that makes no sense at all. A "summoned piercing object" and a "non summoned piercing object" should work the same way. A electricity summoned and a natural electricity should work the same way too. In D&D 3.5, some spells allow SR and some won't allow SR. Like Arc of Lightning, in nwn2 OC i have used this spell against golems. In nwn1, i use the same tactic of IWD since a lot of spells that won't allow SR in PnP like Incendiary Cloud allow in game(by no reason).http://nwn2.wikia.com/wiki/Arc_of_Lightning
I don't know how Magic resistance works in D&D 2.0 and in IWD to be honest, but there are any way to use offensive spells, against Iron Golems and the final boss? There are any "non melee" way to deal with spell immune creatures in IWD? If in my second playthrough i play as a Druid, how can i defeat iron golems?