Have you checked in device manager? Are any resource conflicts apparent? (conflicts with those few devices on a newish machine running XP, are highly unlikely). I would say it could be a driver bug. Have you tried installing the soundcard alone with the lates drivers, and then downloading a different generic driver for the modem and installing that afterwards?
Did you check in your BIOs setup to see if any resources might be reserved?
Try to identify the modem chipset exactly, if you post it up here and any other info you can find on the board I'll try and find you a driver. Also which audigy is it, there are several different kinds? Creative Labs drivers are notorious for being bloated and buggy.
Bookmarks