Firewalling under Debian

[bob parker <bob_parker@dodo.com.au>]

My son's proposed network is to be this:

Firewall / NAT / Gateway machine connected to cable using 1 nic.
Connects to hardware router / switch using 2nd nic.
He has the switch and will be buying a PIII 400 2nd hand for the fw.
We both know it's overkill but spares for PIIIs are cheaper than earlier 
models apparently.

Switch connects to 2 * dual boot Mdk/Win XP machines and 1 network printer.

The fw machine is to run Debian with 2.4 kernel and iptables.
My question is, what is the best way to go about setting up the Debian fw 
machine?

I have the 7 cds for 3.0r1.

Thanks
Bob Parker