Thank you, one and all, who have responded to my post. I have a further question about motion detection. Where is the most reliable place to include motion dection, with the cameras or the DVR? Which is cheaper?
Also, after researching a bit more, I realized that some video capture cards are "stackable," meaning if you want to add more cameras, you can just add another card to your PC. Are these cards as reliable as the "just one card per PC only" ones? I realize that with the PC's we have available right now (PentiumIII, 800Mhz) doing more than four cameras is unrealistic, but if the PC's were upgraded in the future it would be cheaper to put another card in the same computer instead of another card in a different computer.