Do this:
Code:
cat /proc/pci
It sould list the name of the modem somewhere, and give an irq.

Next type:
Code:
dmesg | grep ttyS
It should come up with a list addresses(something like ttyS04), followed by an irq value.
Find the two irq's that match, then type (as root):
[edit]
Code:
ln -s /dev/(address) /dev/modem
[/edit]

Then in kppp, select the device "/dev/modem". If your modem still doesn't work after that, it may be unsupported.