I spent the weekend rebuilding a Lenovo X61 Thinkpad Tablet PC with Vista Ultimate and at one point noticed that the time being displayed was a few minutes off from my other computers. When I tried to sync the time up I kept getting a error with the default Network that the system pings. Busy, I put off the issue to resolve it later, but this morning I noticed that Greg Hughes was having a similar issue. Apparently the default server (time.windows.com) was not working. Greg changed the default server and voila, issue solved.
In case you’re looking for how to do this. Right-click on the clock in the Task Tray, select Adjust Date/Time, select Internet Time, select Change Settings, and pick the server of your choice.