torrent's and p2p programs are not the way to go. I have most the ones you can find thru these and there tampered with. They do ok for a month, so if you just need to be on for a few days or so go for it. best bet is to borrow someones cd, and make a floppy with sata drivers. Some new motherbrds dont need a driver for xp install to sata.
they dont sell xp any more in retail. I found a copy at a small pc shop localy but it was the last one. there also places you can buy a valid cd key online. Just make sure you get the sticker with acid test.
I have not done it, but there are places you can find software to fix xp so that you dont need to register. I have some links to put you on the right path but you realy need to find them yourself. As long as you acctualy look and tried I'll share, but you'll need to pm me.