Comp wont boot up Win XP, says config.sys is corrupted.?

Alright, so a friend of mine accidentally left his computer on during a storm, and it appears a power surge tripped a surge protector, suddenly shutting the computer off. Then when the comp rebooted, Windows XP wouldn't boot up. My friend has been upset, but what details I could gain, Win XP seems to feel config.sys and other important boot files are corrupted. First, is there a way to fix this without an Win XP disk? Second, what in general should he do?