I replaced a modern retail firewall/router with a 500 Mhz Celeron with 512K RAM (Intel 810e motherboard) and a PCI dual port ethernet card of because the 'modern' POS turnkey couldn't handle 100 mbits/second through the WAN interface. The 500Mhz celeron with CentOS5 handled that plus DNS and DHCP without ever cracking 1% CPU usage.
That proves 614K should be enough for anybody.
ah *snap*!
-ML