In my former occupation one of the things I did was to set up a lot of cctv systems, everything from vid surrveillance of the Kingdome to hidden "smoke detector" cameras to catch white collar theives.
This was done using high end video equipment, splitters, time lapse video recorders etc.
It can be done on a PC.
I use a Winfast Deluxe 2000xp tv tuner / capture card here, I have an old RCA b&w ccd camera with NTSC out so it connects right up. I've also done it with a hauppage vid card.
A couple things to keep in mind, if you need high quality video then get big hard drives.
When I record high quality I use up about 1.5GB / hour.
Use an OS that will not get flakey when writing a big open file for hours at a time, and of course one that can open that file after it's closed.
You might want to set up a schedule so you just write 1 hour increments, the Winfast PVR software has a scheduler built in (some cards do & some don't) so it shouldn't be too hard to do this.
The Hauppage PVR card with hardware mpeg encoder & decoder will make your life a lot easier, but it goes for $150 - $200. Still, it's going to perform a lot better than a software solution, you will be able to do better with it & lower quality cpu / memory rather than a cheaper capture card & higher quality cpu / mem.
What I'm saying is, if you had an AMD at 2ghz & 512 megs ddr 400 with a hauppage PVR it would outperform a P4c & 3ghz with faster memory using a cheaper vid capture card due to the hardware mpeg encoder / decoder. It will also record straght to DVD.