Windows XP is a LOT pickier about what it considers ACPI compliant than Win98, and even Win2000. Case in point, my Asus P2B-F installed perfectly as an ACPI board under 98 and 2000, but in XP I had to modify the TXTSETUP.SIF file to force an ACPI install.
If you're determined to install ACPI under XP, here's some required reading:
http://support.microsoft.com/default.as ... US;q216573
http://www.windows2000faq.com/Articles/ ... leID=15300
http://support.microsoft.com/default.as ... US;q224826
http://www.driverguide.com/boards/asus/112.html