I'm using a Acer TravelMate 5720, its definatly not "high end" anymore so they're probably cheap enough on the 2nd hand market. Check that it has a FireWire port (its a 4 pin like most laptops, situated on the left of the body beside a USB). Its got a Texas Instruments OCHI complaint FW chip.. so latencies should be good.
Also Core2Duo 2.0 (T7300 iirc), 2gb ram and a 5400 rpm slow HD :)
-Harry