My wife's PC was running bad, so I am rebuilding it. Installed XP, however now the modem does not work. Seems as though the PC does not recognize it or something. I am in the process of doing MS updates now. That might help, I don't know. All I have for choices is generic modems, but they do not work.

Can you help?

What is the make & model? What type of modem?
Are you looking in the Device Manager? Do you have any Software / Drivers for it?
Did it work previously? Are you on-line (MS Updates) with a different modem?
Are you on a network?