There are three ways to roll:

a) pro-grade DVR (new or used on ebay). These are rock solid reliable and most can be setup in ten minutes or less. Set and forget. Searching for and/or downloading video data can be at best slow and at worst like oral surgery....

b) PC-based systems are the most flexible and user friendly. ESPECIALLY when it comes to searching/finding/viewing/downloading captured video. These are only as good as the PC, so a no-name PC with a $5 power supply may be sitting there dead when you need to playback the bank-robber video. You need to build a server-class machine, the OS (typically Windows) needs to be as stable as possible, and things like RAID mirrored drives are good if you want it to work when you need it to work.

In terms of software, there is commercial stuff like GeoVision or Nuuo, or ZoneMinder. ZoneMinder is neat, but to me it's like soldering together your own smoke detectors vs just buying something that works....it's a good learning exercise, but not for everybody.

c) cheap off-the-shelf DVRs. These are the garden-variety Q-See, Lorex, Clover, Gadspot units that cost about $200. Hit or miss. May run for 20 minutes or 20 years. Software tends to be buggy and typically the video retrieval process can be painful (they don't have much of a processor). But they are cheap and do the job.