Run XP from Boot Camp on Parallel

I installed XP in a VM, and ran perfectly and fast.
I then installed XP in a Boot Camp partition, then created a VM using the installation in the partition. It ran slower.

I was wondering if anyone had the same problem or maybe there is a setting that I'm missing. I'm new to this so if you could point me to the best option I would appreciate it.

I have the new macbook with 2 GHZ, 2GB of Ram, 160 GB HD