Unfortunately I do not have any experience with CCTV although it is certainly an interesting topic.
I believe you can purchase analog capture cards which have say 4 dedicated coax inputs for CCTV cameras and I would think would include the necessary PC software to record all simultaneously with time/date stamps etc.
I would think that this is expensive although I have not researched it. Of course the latest thing is IP cameras, CCTV cameras which can be connected to an ethernet network and the video is transmitted using IP. Handy for new installations as companies seem to want to move away from having a central security room where normal camera feeds would be wired too.
Apparently with IP cameras, you run a server which can receive the video and which due to the nature of networking can be remotely monitored, accessed etc.
You could also just use an analog TV capture card for your existing set up, but this will only support one channel input at a time and the bundled software will be designed to facilitate watching TV and basic recording, so may not be advanced enough to capture the video as you would like in terms of multiple cameras and stamping.