What is the best linux firewall?

what is the best free linux firewall that allows for vpn, web filtering, web hosting and that will run good on an old computer with 256mb of ram and a 40gb hard drive and two nics?

I want to protect my home network that has 2 windows servers 2003r2 and 7 windows 7 pcs.

my question is will that slow my network down on that old of a pc? The nic in the pc are 100mbps and thats what my network speed is also ADSL, im thinking it should be fine but want to hear what you think also.