SNF allows you to use only ttyS0 through ttyS3 (COM0 - COM3) for modem port. It makes it impossible to use PCI modems because serial driver assigns for them COMx numbers starting from 5 (COM5 etc) i.e. ttyS4, ...
The same bug has been present in DrakX and has been "fixed" by allowing 8 COM ports instead of 4 (the correct fix is to check for available ports but the above would be O.K. for most users). -andrej