I have a Dell optiplex GX260 that I recently aquired for $50.00. The labels on the computer says it has intel pentium 4 and windows xp. However someone previously removed xp and installed windows 2000. I have not been able to use the computer because I do not know any of the windows passwords. I tried several password recovery/ cracks to no avail. I would like to reformat the hard drive and install windows xp. I have a copy of a Dell operating system disc with XP Pro, still in a sealed envelope. I know that this operating system should load onto any Dell computer. My question is do I use the product key that is on the computer I am installing the operating system on, or do I use the product key from the machine that the Dell operating system disc came with? Also, what is the easiest way to reformat the hard drive prior to installing the new xp operating system?