Ok look my windows got messed up and I had to reinstall on but I didnt have a disk of my own so I borrowed my friends. Now I have t activate it on my comp or they won't let me use it. I got the product key from her but when i called to activate they said it couldn't be on 2 omputers at once. Fine, can anyone tell me the cheapest way to fix my problem. It is said i can get a new product key, but how and how much will it cost.

your best bet would be to get a key from microsoft. they might charge you a full retail price of xp. around $200.
your best bet would be to get an o.e.m. cd that has c.o.a. (certificate of authenticity), cd-key and is a legit ms product. you can get one from here:
www.softwareoutlet.com
it costs about $79.00.