How much ram do you have? 768mb's of ram is working for me.
Although, i'm not nessecarly used to speed, my previous mac was a 200mhz w/ a sonnet upgrade to (700?)mhz, and had 128mb's of ram. And my linux computer was a Quadra650 (33mhz 64mb's of ram =).
And i dont run games like WoW, i ocasionly use Starcraft, or the halo demo, so i don't know the amount of ram it eats.
Maybe you can try quitting the finder when you play WoW? I found it made my speed in WCIII 2x times faster.