I'm not a gamer. Initially I had Boot Camp and then tried to install Parallels - which came easily. My problem was Windows activiation - just like yours.

Basically, I just binned Boot Camp and ran my WinXP Pro in Parallels. I had to telephone Microsoft and explained what happened and they were really helpful.

I've not looked back since. I've copied the original XPPro.hdd and can swap it backwards and forwards off a back up hard drive - each with different software on depending on what I want to use (this keeps the Parallels hdd file smaller too).