For that hardware, a FireWire DV video converter and a large hard disk are the best. DV video is not very CPU-intensive, so it's better for slower machines.
PC capture cards won't work in Macs, the drivers aren't available.
Some of the USB devices that have hardware MPEG2 encoding work quite well, but of course MPEG is terrible for editing, if that's something you plan to do. (DV was designed for editing.)
tooki
P.S. This belongs in Peripherals.