I haven't tried this driver yet, but I had such a hard time finding it, that I'm posting it regardless.
This is for the "modem riser" that is included with the PC Chips m599 motherboard. This is for Windows XP. This modem riser was manufactured by PCTel and bundled with PC Chips motherboards, or so it appears.
There's a picture of this modem at the bottom of the page at the link above.
Already tried it? Give your review.