NetMAX Firewall is a relatively inexpensive program (approximately $80), it
is Linux based (very stable) and can be administered through a web browser.
I use it at home with a network of 8 computers (2 Mac, 1 SPARC, 2 NT, 2
win98 and 1 Be). It seems to work quite well and setup was relatively
painless (I run it on a Pentium 100 with 32MB RAM and a 1.5 GB hard drive).
Hope this helps.