Run kppp. Click 'setup'. Click 'device'. Choose device (ttyS0,ttyS1). Click 'Query Modem'. If you get 'modem not responding', then choose a different device. If you get 'modem is busy', then your modem is probably a winmodem. If you get a bunch of stuff from the modem (it's name, etc), then you have a very easy to use hardware modem.
For winmodems, go to www.linmodems.org