Help with video surveillance systems

Hello, all. I urgently need advice about what kind of video surveillance system to get. Our building is under attack by thieves (car stolen out of the garage last night), and we want to make sure we have the building's common areas recorded. We have video footage of the two people who stole the car because there was already a camera in the garage, but we need more cameras to track movement inside the building if it happens again. We need a 6-8 camera system with the best black + white, low-light cameras we can find. The video should be recorded onto a hard disk (existing computer, probably).

Any tips? Thank you!