Sharing out Internet via RCA cable modem

I’ve got AT&T broadband providing service via an RCA cable modem (model DCM225), and I haven’t yet shared it out via Windows; that looks simple enough BUT on the RCA website there appears to be no Linux/Unix drivers. I’m using Red Hat 7.3 on a partition, and have three other Linux boxes to share out to, but it doesn’t ‘see’ the cable modem (it does list the USB device in Nautilus). Please advise on getting Red Hat to see it, or where I might obtain an appropriate driver for the modem. Or, how do set up a separate server to share out the web to both Windows AND Linux boxes. Thanks!