Alright you Linux-heads...

I've got a couple of 486 boxen (25 mHz, 8-megs of Ram, 1.2 gig hard drive) sitting around the house. I'd like to make one of them into a Linux-based firewall for my cable modem. (I also have a copy of Turbo Linux available for this project) Currently I use both a PC and a Mac, and switch between them via a KVM switch. Both are equipped with Ethernet cards to connect into the cable modem. I've tried using an Ethernet cable switch to select either the PC or the Mac, but it didn't quite work the way I expected it to. At the very minimum, I would like to be able to * have both the PC and Mac be able to access the internet at the same time * do the usual firewall stuff (e.g. keep the bad guy out. I currently use ZoneAlarm on the pc, and it does a decent job) I'd also like to go further, and have the Mac and PC read each other's hard drives (still, while keeping outside users out) What do I need to do/get here? Thanks!