The online download portraits are TGAs, I believe, and can be reformatted with Irfanview (which is free; there's a link in the forum guide to SodiPodi). For example, I just converted some elf (Aerie?) into GIF:
Alas, Daedrous, I haven't played NWN for quite some time. I believe my login is LoopyZebra, though. I just remembered the mods on that site.