Yes you need a video input device. And just so you know, the M10k sucks big time with CPU intensive tasks. I am sure Centrafuse is tasking it to the max already. This means you cannot use the el cheapo $20 usb/pci card. You need one with a dedicated hardware encoder/decoder chip so it doesnt bog down the CPU, but that gets expensive fast. Usually price is a good indicator of how parasitic it is.
Also there have been posts around that use a seperate hardware box to overlay GPS speed or text of somesort and record to a tape or harddrive or something without the PC. Not sure you reason for wanting to record, but if it is for fighting tickets, independant with overlay is the way to go.
If just for a backup cam, it is not worth the hassle with the M10. The performance hit of writing a stream to the HD as well as video processing far outweighs the "cool" factor.