Thats a nice setup. I would recommend going 64 bit though and if you can stretch the budget, drop back the speed of the RAM and go for 8gig instead. This will be much more useful than 4gig of 2GHz stuff. I wouldn't worry about having 5 separate installs of WoW on the raid, just load it from the one folder. If you want extra speed you can still add in a $200 32GB SSD for symlinking the data file in the future if you want, but raided raptors are very nice.

Cheers