I have installed the windows 7 RC build 7100 and was wondering if when the time comes around when I decide to purchase windows 7 after it is released if I have to do a clean install or just a "upgrade" to get it to run. If I need to do a clean install then I would like some heads up before I wipe everything.

Thanks all!
I beleive that there is s a work around for this but I'm not sure what it is. However if you're not comfortable with doing that and are just going to put the disk in then yes, as I understand it you need to do a clean install and should back up everything first

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Here we go, found the work around:
http://windowsitpro.com/article/articleid/101865/upgrade-of-windows-7-beta-to-rc-and-rtm-to-require-some-mucking-about.html

Hope that helps,
Bob