Outlook Calendar & Citrix

Some of the staff in my company are experiencing an issue where their Outlook calendar, when logged in through Citrix, is an hour off. Consequently, we are running the risk of people missing appointments because the calendar is showing the wrong time. This is not happening to everyone and for one person its correct when they are in one office, but wrong when they are in another office (all of our offices are in the same time zone). It seems very random, only some users and only in certain offices and that is somewhat confusing to me. We are using Exchange 2000 with Windows XP Pro clients and Citrix Presentation Server Client 9.0. Thanks for any suggestions.