If you want current technology (v.90 or .92, etc.) you probably should consider an external serial modem as most of the cheap PCI modems these days require more processor than that. There is a Cendyne on acortech.com and other sites which is the one I use and is less than $20. shipped and it comes with everything you need. There is also a way to even get reduced shipping on it sometimes if you look around.
. Just be aware that Cendyne is OOB, so your only backup is acortech or whoever you buy from (largely just DOA protection). The actual mfr. is
http://www.amigo.com.tw and it has been sold under many names (I think newegg still sells it under a couple different names and for more $$$), so there are places to get drivers, but they haven't been updated at all (at least as of the last time I looked). IAC, external modems are better for the reasons I enumerate in that thread. Most important among them for your situation is that it puts no load on the system CPU.
. I have an extensive thread on it over at
http://www.techimo.com in the appropriate section and most of the info is also in the review that I did of it in the "User Reviews" section on the same site.
.bh.