Download W7 RTM, just check MD5 to make sure You get untouched version and use it without a key for 30 days, then use rearm function to get another 30 days, you can do this uptto 3 times giving total up to 120 days use without key. When W7 hits retail shelves buy Yourself a copy and use key from that to activate Windows. Make sure you install the same version You are intending to buy. Yuo might need to modify RTM disk to install version You want.