It can be quite difficult to advise at this sort of distance as we don't see what you see. I'll assume you've got a clean XP system built and the only device not seen by windows is the Ethernet Controller (other than the PCMCIA adapter).
So XP is behaving correctly. You can run MSCONFIG 9if you haven't already done so) and invoke Network Diagnostics in the TOOLS menu.
Presumably you know what network adaptor to expect (like Broadcom NetXtreme 57xx) or whatever is on your laptop's board. If the device isn't there, then I'd suggest it's faulty. It might even be the reason that your client wanted the laptop rebuilt and he/she didn't tell you that - but that's me being cynical.
You've no doubt done all the normal stunts like booting indo "DOS" with networking, going into Safe Mode, etc.
Anyway, I'd say you have a way forward with your client - particularly as he can pay for a PCMCIA adapter as his/her on-board adapter is non-functioning.
Before writing that off, is the green light on at the LAN port? Or is it dead (which is what I'd think it to be).
Good luck.
