Some of our forum goers have noticed that Microsoft 2010 has not been supported on XP 64bit. Microsoft have made a statement to Arstechnica on the matter.
“For the Microsoft Office 2010 release, we will not support Windows XP 64-bit. For the best productivity and user experience, the benefits of 64-bit computing with Office 2010 is best experienced by utilizing the newly introduced 64-bit version of Office 2010 with Windows 7 (64-bit) or Windows Vista (64-bit) version.”
Read it in more detail over here.