I would contact Microsoft Technical Support and ask them. I will cost about $35.00 per incident but if you need it, you need it.

Before doing this I would check Microsoft's knowledge base under searchwords 'XP' and 'installation.' Someone else might be having the same problem as you. You might be able to find a write-up about your problem there.
The website is:http://search.support.microsoft.com/kb/c.asp?fr=0&SD=GN&LN=EN-US