Update: With Team Foundation Server 2010, you no longer need to download and run the TFSVersionDetection.exe tool as this functionality is baked into the Team Foundation Server administration console. See this post for more detail: http://blogs.msdn.com/bharry/archive/2010/05/07/extending-trials-of-tfs-2010.aspx

As with Team Foundation Server 2005, we are publishing a utility that you can run on your TFS 2008 server to determine what version of TFS it is and, if it is trial, how many days remain until it expires.  It also enables you to extend trials by 30 days.

The program is called TFSVersionDetection.exe and is attached to this blog post (see the link at the bottom of this post).  I recommend that you run the tool on the TFS server itself.  You can run it from another machine and point it at the TFS server but it does a less thorough job of detection (due to permissions issues, etc).  If you run it on the TFS server and press the "Check" button, you will see a screen that look something like the following.

TFSVersionDetection

If you are within 10 days of expiration of a Trial Edition install, an "Extend" button will show up in the lower left hand corner.  Pressing it will extend the expiration another 30 days.  The "Extend" button will show up again when your 30-day extension nears an end.  Pressing it at this point will bring up a dialog that asks for a new Trial ID.  It is possible to extend it another 30 days if absolutely necessary.  To do this, you will need to contact your Microsoft sales rep and ask them to help you get a new Trial ID.  You will need to supply your existing Trial ID when contacting us; this existing Trial ID is displayed by the version detection tool.  If your sales rep doesn't understand the process, they can email tfstrialsupport@microsoft.com and we will help them.

Brian