Router/firewall with gateway a/v protection?

I was recently thinking about converting my extra PC to a firewall/router using one of the free programs lik smoothwall. But im not sure I am up for the chalenge just yet. We recently got a Sonicwall firewall at my job and i saw that it has gateway anitvirus/antispyware/antispam built right into the router/firewall. Is there anything like this made for home use that doesnt cost thousands of dollars?? I see that Sonicwall makes the SAVR 80 which isnt to expensive but it only offers 10mbps throughput with the antivirus turned on. I have a 30/5 cable connection so 10mb throughput just isnt going to cut it. Anyonje make something similar with more throughput? Or if I descide to use my spare PC(amd3800/2gig) is there any software that will do this and offer better than 10mbps throughput with gateway a/v enabled??
Thanks