If you have the Windows ME disc and a product key for it, you could try that, just to prove if the Hard disk works, but there will be several real problems. Microsoft don't support ME any more, so that it will produce many errors, also I believe Win ME didn't work with hard drives over about 130GB. It would work, to an extent, but does not compare to Vista or 7. You can use XP home or Pro for several more years, it's fine. If you can see the BIOS screen when you boot the PC,(press F2) and you can see the name and type of the new hard drive listed, make it second in the list, and make the CD/DVD first. The disc you need to install XP from must be an operating system disc, rather than a recovery disc, it's not the same thing. You also need to have a 'product key', which can be keyed in, part way through installation. The bad news is that, unless you bought your Windows XP disc from a retailer, (on-line or shop), it won't work for more than 30 days, or to the point where you try to activate it. Your choices are, 1, to install XP every 30 days, or 2, Buy a new Windows 7 O.S, with new product key, which will be good for the next 5 years. I hope this makes sense !