Need advise for a linux firewall

[voipuser at optonline.net (Abdul Nazeer)]

Looking for advise on setting up a linux based dedicated firewall.
Apparently, there are plenty:

http://en.wikipedia.org/wiki/List_of_router_or_firewall_distributions

I'm looking to have the firewall sit in front of a public network of
windows boxes. Also, would want to be able to load-balance and re-shape
traffic inside the network. I was hoping to accomplish this using
iptables, but if anyone has any other suggestion, I'd love to hear it.

Thanks!
Abdul Nazeer