My system is a bit weaker on CPU power with a Q6700 2.66GHz C2Q. I do have 8GB RAM and 64bit Vista though. I doubt you have a hardware problem.

I'd recommend that you grab Process Explorer from Microsoft's free offers and use that to look a bit closer. It's basically a much more detailed task manager view for your purposes.

Make sure you look at your CPU load per core AFTER you have logged in and finished loading the zone. WoW has insane CPU consumption on the login screen and CPU load may be higher when the zone is being loaded. I split my five WoWs between the cores, each client using one core, with the exception of 4 and 5 which share one. I use two WoW folders, one with max settings and resolution for the main and one with minimal settings and resolution for the secondaries.

I hope this helps.