Help configuring laptop and dialup Inet gateway

[scott at ehrlichtronics.com (Scott Ehrlich)]

I want to experiment with configuring my laptop (I plan to put Debian on
it) with modem as a dialup Internet gateway to help bypass my cell phone
provider's data charges and turn my home number into an ISP.  I'd also get
a data/voice detector for the line.

OS/application-wise, what would I need to do, specifically, to get this up
and running?

I have a cable modem connected to a Linksys befsr81 broadband device, then
my PCs branch off that.

Thanks.

Scott