FYI to everyone who wants to try this. I was told it would not work but it did for me. I picked up 3 HP desktops one being a DC7700 and two similar units all the same design. All 3 had different issues and all needed a fresh install of the OS XP PRO. The issue is that I only had my DELL CD. I could not find an HP version. I went into the bios screen, via F10, and changed the boot order for the CD ROM at the top of the list. From there SAVE AND EXIT. System rebooted to the LOGO screen then to the usual BLACK screen. "PRESS ANY KEY" at the top. From there the CD was read, installed, and activated as NORMAL. Exactly as it would in any DELL. It did NOT ask for a product key. Many forums/articles said the existing COA from each tower could be used but ONLY if it asks for one. I do not have a DELL COA other than the code on the CD seleeve which is NOT a COA. All 3 towers are up and running. I don't need an HP cd apparently. No issues at all. I suspect that this process will work for any tower, just as a retail version is supposed to do the same thing. This is the way it SHOULD be!. Simple and straight forward. No games or BS.