That really depends on the type of cameras you are using also. The system can only record the "best" quality of video it is given. We personally use Vicon systems, which are Windows XP based, and allow for an amazing amount of support for networking, Video Analitics, etc. We use Everfocus for our lower-end customers and they run about 3k for a decent system. They are Linux OS based, and reliable as a rock. The OS is actually on a chip, so even if the drives die, the system stays "in-Tact". It's really on personal prefrence. At home, I use an older Intellex DVMS system, and it works just fine. Compare a Dodge Neon, to a Viper. Better cards= better frame rate= happy customers.
Cheers
J