Johns=GCHQ= wrote:
you can use other discs if they are the same os, like home, prof. and use the serial key that the system is installed with. if you dont no it theres loads of ways to find out. just google it
He's right just use any xp disk with the same version (e.g if your using pro get any pro disk) with the current key found out via the registry or the magic jelly bean key finder. Then install and activate as normal.
Might have to phone for activation, when they tell the conformation code they'll try keep you on for longer but just hang up and press next.
Works for me.