"Enable DirectX Shaders (experimental)"
Was this listed under Video in configuration mode? If so, I turned it on.
Also, I find it strange that my iMac currently struggles with WoW, a 2.4Ghz C2D shouldn't really struggle with such an old game, right? Having about 60-70% actual CPU load with only the game running.
I'm using a quite fresh installment TinyXP, so there are not alot of background services running either.