How do I get around registering windows xp professional?

OK.. so I was given a computer with that was wiped clean (had Linox on it).. and given the windows xp install cd (with service pack 2 included)... the activation key I was told went with the system will not work anymore... windows is installed and works fine, but I have to register in like 14 days! What can I do to disable and NEVER have to register.. I don't care about updates. Anyone know how I can do this. I'm really computer literate... so hit me with it :P