make sure that your XP guests are picking up their time from the PDC emulator for the domain. and make sure that your PDC emulator has its timesource correctly configured.
Tom Howarth
VMware Communities User Moderator
Tom Howarth VCP / VCAP / vExpert
VMware Communities User Moderator
Blog: http://www.planetvm.net
Contributing author on VMware vSphere and Virtual Infrastructure Security: Securing ESX and the Virtual Environment
Contributing author on VCP VMware Certified Professional on VSphere 4 Study Guide: Exam VCP-410