Or you could combine a linux distro (such as www.ipcop.org) and a Mini-ITX box (www.mini-itx.com) which is my longer-term plan.

Currently I use IPCop running on a old compaq P100, 16MB machine with a 1GB disc. Unfortunatley, whilst it's performant, it's too noisy.

My plan is to go to a mini-itx (probably EPIA 500, which is fanless) system for size and noise as you say. (See linitx.com - check out the 'light' system)

Paul.