There is a KnowledgeBase article on this very topic. Here you go:
http://support.microsoft.com/default.aspx?scid=kb;EN-US;q224071
It has how to move any of the databases, whether user or system. For tempdb, basically it's as simple as a couple of ALTER DATABASE commands and a stop and restart.
K. Brian Kelley
http://www.sqlservercentral.com/columnists/bkelley/
K. Brian Kelley
@kbriankelley