After Wayne's recommendation I bought one of those Lenovo Thinkcentre A61e USFF thingies. He's not kidding about expansion options - no PCI slots! I think there is a mico-PCI slot free next to the (laptop) memory slot, so WiFi is possible. On the back there are 3 audio ports, 4 USB, 1 Ethernet, one VGA and the DC power socket.
That low price of £195.73 + VAT (=£229.98) also includes a sturdy keyboard, a very lightweight optical mouse, and an XP licence, but no CDs and no monitor. The concept is not far off a MacMini, but about three times larger, and black. I'll be installing Hardly Heroin when it's released at the end of the week, and I'll let you know how it goes.
Regards, Tim Green.