os

I collect and find TOWERS for me to test, repair, and/or give away to people who need/want them. My question is simple, although I think I already know the answer. Most of the towers are loaded with windows 95 through xp. Is there a way I can remove an older os and replace it with xp pro all from the web/net and make it work with the tower at hand which would include downloading any drivers for the cards if needed. I do not have the expertise to wipe a hard drive, nor do I have a copy of xp pro on disc, genuine or not. Can this be done? Any links, web addresses, ect will be welcome. I have a tech friend who does this for me, but the lead time can be long. He also thinks I would have a hard time doing this even if I HAD a disc. Any help offered will be welcome. Is there a XP PRO "LIKE/CLONE" os that I can use? I use ABI WORD, which is very similar to MICROSOFT "WORD" that is downloaded from the net. I have OFFICE 97 on disc but the disc asks for an 11 digit code that would be on the disc packaging that I do not have even though the disc is genuine. There must be a better way.