The ISO is just the Service Pack3 (which you need anyway, but don't worry at the moment. I think BD was stating you may be able to Repair Windows indirectly via this, I don't recommend it, on this issue, backups to do and all)
Lets go back a bit (the posts are getting way out of hand!)
You need the XP CD (That is final)
Either purchase/locate or borrow (note: purchase is preferred)
I have already provided link to newegg (somewhere up there!) to get XP
You need to be aware that XP CD will soon not be available at all !!! ie Purchase it.
Once you have the Windows XP CD with the product key to match, then reply back.
You can backup (to CD or DVD) in the mean time
End of story