I used to have a lot of problems with internal modems back in the day of those stupid idiotic WinModems when Windows 95 was out because I always had dual boot systems with Win 95 on one partition and NT 4 on another.
Since then I made the switch to external modems connected to COM2, IRQ3 and haven't had any problems. I've known a lot of people that have had issues with internal modems and my advice is always the same - ditch it and get an external modem. I like 3COM but I'm sure most of them will work fine.
Isn't there a forum for these kinds of questions that would be better suited than the bargain basement?