Core 2 Quad compatibility with windows xp

I have a Phenom 9950 Quad-Core, with windows xp. As I read some time ago by the Internet, said that XP could only pull 2 processor, so do not take advantage of the Quad 4. The issue is that if I go to device manager, I get the 4 processors, but if you step on Everest, and still the route processor CPU Properties - processor type, I put 2x, 2600 MHz, so do not understand that if only recognizes 2.
Conversely, if I look a little further down, in particular ---- Processor CPU usage, what I see is:
CPU # 1 / Core # 1
CPU # 1 / Core # 2
CPU # 1 / Core # 3
CPU # 1 / Core # 4
and beside each, a figure which rises or falls depending on the CPU usage.
Are you using Xp or not the 4 processors? Be better with Windows Vista?

Thanks to all.

Windows XP Home supports as many cores as you squeeze into one socket. WindowsXP Pro supports as many cores as you can squeeze into two sockets. Thus... a quad core CPU will work on both XP Home & XP Pro.

Yes, Windows XP will work with Quad Core CPU's. Instead of just removing Vista, you can try a dual-boot system so you can use both Vista and XP. Stick 4 Gb of decent ram in the system ... my best recommendation for a workhorse system that your building. Get low latency RAM - DDR2-800.

Quad-Core is better utilized on the XP Pro OS better than any Vista to date, in the same power usage but with better multi-core usage in many Independent tests.