Stay with XP. Even if you buy a new computer with new hardware, XP will use it better, you will have a blazing fast PC compared to Vista. Take RAM usage for example: just booting the OS and going to task manager you will see a 250MB RAM usage on XP and 800MB Ram usage on Vista. Now even if you have 2GB there's plenty of RAM wasted only to give you eye-candy effects and slowing down CPU.

Also, hardware-assisted audio from Vista is compromised, without special drivers, cards like Creative X-Fi or Audigy can't use the special hardware features under Vista.