its gonna be hard unless you've got a serial modem or a hardware pci modem. If you got a winmodem it may not be supported. boot to windows goto
www.linmodems.org. your best bet is to get a serial modem not usb use kppp or wvdial. your modem device will be /dev/ttyS0 or /dev/modem which is a symlink to /dev/ttyS0