I've been running Untangle for at least a couple of years on a Dell 1750 server (Pentium 4 3.2GHz & 1Gb RAM) for home use without any problems on a 8Mbit broadband connection. ($50 on EBay !)
In a few weeks time I'm switching over to fiber broadband which should give around a 76Mbit connection (Hurray)..., so do you think my current tin is up to the job (supporting 3-5 internal users) ?