http://madeformediacenter.com

http://madeformediacenter.com/m4mc/app.aspx?id=f57f787f-a8d4-4acf-9e5a-685627c8cd46 or http://www.missingremote.com/news/2011-01-31/wmc7-tv-recording-schedule-backup will let you save your series info.  You can use Window 7’s backup and restore to move a bunch of stuff too.

The big concern without doing a clean install will be that all the drivers get redone.  When the system tries to redo the Northbridge/Southbridge drivers will be potential choke point.  Your power management, PCI controllers, memory controller, IDE/SATA controllers, etc are all going to change.  I have read about people successfully getting Windows 7 (and older builds of Windows) to work afterwards.  I’ve also known it to result in systems that appear to work but are unstable and have data corruption.  I’ll be curious how your attempt works and hope it goes on the good side.