Upgrade TFS from the Trial edition to a licensed copy...

If you were an early adopter and/or just testing out Team Foundation Server 2008 and now want to upgrade to a licensed copy without reinstalling on new hardware see this MSDN article for the appropriate steps: http://msdn2.microsoft.com/en-us/library/ms404852.aspx

(Note if you are a Volume Licensed customer, you may need to call product support because you will not have a Product Key in this case.)