Using Server 2k3 as Router/Firewall

Over the past 3 weeks Ive gone through 2 DOA and one just non functioning WG Firebox firewall. Though I didnt purchase these, they seem to have some nice features for the price (VPN, WAN Failover) Well since 0 of the 3 have worked so far, Im considering taking on old PC and setting up server 2k3 on it with a couple of NIC cards and using it for this. Can anyone give me any disadvantages to this or recommend better software to use for this other than win server? BTW i understand software routing will generally be slower than hardware but I only need to support 50 internet connections tops. I also will be supporting a e-mail server(50 users) and an FTP server.