Biostar M7VIT Problem

My Biostar M7VIP recently went bad under warranty, and was replaced with the M7VIT. I updated my Bios, and loaded Windows Professional 2000, which recognized my video (e-GForce4, 64MB) and my modem (Agere Soft Modem). The problem is that when I go to test diagnostics on the modem I get the error "OpenComm" 'Can't open Port'. So I blasted Win2K and loaded Windows 98 SE (under which this modem worked fine) - and I get the same error.

Help! Anyone have any ideas? The Biostar people were hopeless, and the place I bought the hardware kept my system for 2 weeks before returning it to me like this - I'm not keen on the idea of taking it back if I can fix this myself.

Thanks in advance for any help you can give me
Roben