win xp installation failed

hello there...maybe you can help me out here. i had windows 2000 professional installed on my computer, but wanted to try windows xp professional. a friend of mine gave me a copy of his and i tried to upgrade my OS to XP. upon installation, an error message came up and installation can not complete anymore. i do not want XP anymore. now when i start up my computer though, XP set up automatically loads and asks for the CD to complete installation. i dont want to do this because i do not want XP and it does not install anyway. now i have no access to my computer at all......is there any way i can start up windows 2000 again?????????????????

 

i also do not have my windows 2000 pro cd anymore.....can anyone help me out here....must salvage computer before school begins.....

 

i also have not used this computer really at all, got it from my dads office, intel celeron 1.3ghz 40gb 128ram, came originally with win98, tried to upgrade to 2000 then it crashed after install becaus ei had no drivers, then a repair man fixed the problem and installed all new drivers and 2000professional......my friend actually got the copy off of the internet, said it worked for him...now i am stuck with a computer that only goes as far as the win xp installation screen and i can not do anythign from there with the cd i have, the message says there is a problem with a manifest document or somethign and that a cfile does not match it and install can not complete, is there anyway i can get back to windows 2000 since xp was not installed, just the install was initiated/...