Had to deal with this one? I have… just recently in fact.
I received my complimentary Product Key from Microsoft (thanks to the InstallFest put on by Joe Healy and Jeff Barnes of said company!) and couldn’t figure out where in the heck to put it. Then I put it down for a few weeks until this evening when I got the dreaded "this trial will expire in blah blah blah blah blah…" you get the picture.
Well, I did some digging and found the ray of hope; it’s on MSDN at this URL. Turns out the way to paradise is through your Control Panel. The instructions are written for Visual Studio 2005 and Windows XP, but they work just fine for Vista and Visual Studio 2008. My adaptation of the instructions are listed below, with PICTURES!. Oh, and the MSDN instructions are italicized; my comments are not.
To upgrade Visual Studio
2005 2008 Trial Edition
On the Start menu, click Control Panel.
Select Microsoft Visual Studio
20052008 Professional and then click Change/Remove.
On the Visual Studio
20052008 Maintenance screen, enter the Product Key in the section Upgrade to Visual Studio 20052008 Professional and then click Upgrade.
There should be 5 Product Key boxes in the lower left hand corner of the second image below but I got way too happy with my CTRL + C (dang it!). The second image is what you’ll see working your way through the Uninstall/Change process. The second image is the "all done, all good" confirmation.
Any questions? Let me know.