Pulled from Microsoft's website:
"Sorry, the Windows 7 RC is no longer available for download. If you’ve got the download and need a product key, they’ll be available until October 21, 2009."
You can still get a product key for either 32 or 64bit Windows 7 RC from this site:
http://www.microsoft.com/windows/win.../download.aspx
However you need to find a Windows 7 RC1 Build 7100 installation disc. Ask your friends or look for an .iso online. Once that's all done just insert the Windows 7 disc into the machine and choose the boot from cd option when after the machine posts. Click install and enter your key, format the old hard drive before you tell it where to install Windows 7 the option to do this is given during the install process. Hope this helps and good luck on finding your Windows 7 install disk.
-ZEROKOOL