Outlook Calendar Issues

I have several employees sharing their Outlook Calendars. We are using Outlook 03 and 07 and for some reason some of the times on the Calendars are different. For instance, an employee using Outlook 2003 will see a Outlook 2007 Calendar one hour ahead. I know that this has be an issue with DST but I have updated both XP updates and Outlook 07 and 03 updates but still the same issue. Has anyone ran into this issue?