Jward52,
As Wolfie2k6 stated that while we do not know if Windows7RC will be offered in "uprade" or "full" versions as that information has not been released at this time, it would be best to perform a clean install as opposed to an upgrade. Please remember, the RC will expire June 1, 2010, and the bi-hourly shutdowns will begin on March 1, 2010. You’ll need to rebuild your test PC to replace the OS and reinstall all your programs and data.
I would recommend that you perform regular backup in prepartation for the swtich next year. For more information head on over to Microsoft Springboard for tricks, tips, videos and more!
http://tinyurl.com/832nco
Jessica
Microsoft TechNet / Springboard