Someone performed a "safe re-install" of XP Pro on top of XP Home

A customer of mine thought they'd save some money and perform a repair install.... however, the Dell tower had XP Home installed, and he used an XP Pro disc, so naturally everything in Add/Remove Programs has disappeared (the programs are technically still there), all the user accounts and their data is gone (again, they're still technically there but not accessible in the current state), etc. I can resurrect the user accounts and the data within, but how can I restore the functionality of all the programs and get 'em to show up in Add/Remove Programs? Is it even possible?

THX!

(had he brought me the PC before attempting his own "repair", he would have actually saved 1-2 hours of labor charges; but know I have a lot of extra work to do that I wouldn't have had to do in the first place :banghead )