"I don't have the disk anymore"... Why not? We do NOT support piracy on the MacNN forums, and will not enable or provide instruction for those who want to pirate.
And unfortunately, you NEED to have the XP disc, because you NEED to copy files from it to restore your installation. Assuming you've lost your legitimate disc and I'm jumping to conclusions above, you will still need to obtain a valid copy of XP at least as new as the one you used for your installation to fix this problem.