Need help about installing windows 7 (Pre-orders)

Ok I'm totally confused right now, I looked at other threads and I find it hard to understand so I'll just ask and make another new thread cuz the Pre-order sale is almost over and I have to buy it before it becomes 199.. so Here it goes

I have a Win7 64bit RC ATM and I'm willing to get the windows 7 professional from Newegg (99 dollars Pre-order)

I heard that you can't install those upgrades without having an XP or a vista....

I have a Windows XP Media Center Edition 2005 32bit, and I used it before to install win7 RC.

My question is:
Will I be able to install win7?
Do I have to format my HDD and Install the OS?
Do I have to install my XP and then install the win7 that I bought?

Thanks for your time :)

supposedly, from the rep I talked to from microsoft, I was told that I'd be able to upgrade from win7 rc, my personal advice would be to do a work around clean install, there's so many updates and such for win7rc thatit could screw up your install and it'll be more of a headache in the long run... don't worry about all the hoopla and just get the upgrade, if it doesn't work out, you could always sell it on ebay or something...

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