thanks for the posting
Thanks for your posting I was able to install XP over Vista. The steps I went through:
1) Powered up computer and immediately press F2 to enter BIOS
2) Changed boot sequence to have "Boot from CD-rom" on top of the list
3) Changed the Flash Cache Mode to "Off"
4) Changed Sata Operation from AHCI (default) to ATA
5) Save the setting and exit bios
Now the system should boot from Windows XP CD. After finish installing XP, went back to re-enable to Flash Cache Mode back to "enabled" or "on" (forgot the exact word).