What processor speed? ANything over 1Gig should be good.
I have used several G4 laptops with an IO for uncompressed SD footage. It works great. You will need a PCMCIA card adaptor hooked to to a 2 drive SATA raid if you need to move to 10 bit uncompressed, but you can get away with a FW800 PCMCIA adaptor and a FW800 raid0 array (such a 2 drive GRaid or Lacie array) for 8 bit stuff. SATA is cheaper and faster, none of them are secure as they are all raid0.