The software is commercial grade, but it does come with a few issues.....
First you need a server to run it on, doesn't have to be new hardware but something powerful enough to run a LAMP server on (Linux, Apache, mySQL, PHP) and of course Zoneminder.
This server can and should run headless and be remotely administered so it can go in any closet or wherever out of the way, the server can be accessed via SSH and Zoneminder uses a web interface so anywhere on your network it can be administrated along with the database it creates/uses in mySQL.
So my setup (a work in progress)
I'm running the server which is fairly new hardware in a server rack along with a couple other servers, it's a AMD 6300 CPU with 16gig of RAM, probably way overkill for just the CCTV aspect but the server has other things to do so I wanted to cover all the bases. I tested the system on a old AMD phenom quad core system and it ran just fine.
Network: even though I have a gigabit network the IP cameras are 10/100 which is just fine for the data stream, depending on the cameras you use and their placement (more about that later) you may want to consider IP cameras that use POE (power over ethernet) because they greatly simplify the wiring down to just the cat5e cable to provide data and power, power can be provided either using a POE injector for each camera or a POE switch to provide data connection and camera power. Since the number of cameras I will eventually have installed will be around 14-18 total I opted to buy a Netgear managed POE 24 port switch that is capable of powering all 24 ports with POE power. If you were only running 2-4 cameras the POE injectors would work but a good unit is around $18-25 ea so it adds up quickly.
Cameras: IP cameras come in a lot of price ranges, I have found that the average cost for a decent IP camera (bullet type) is around $95-$150 ea of course these are POE cameras which is what I needed a couple good brands that are easy to setup in Zoneminder are Trendnet, and Hikvision, the problem with Zoneminder is that you have to check the compatibility of cameras before you buy while theoretically any IP camera can be made to work the amount of time it takes is more than I want to invest.
http://www.zoneminder.com/wiki/index.php/Hardware_Compatibility_List#Network_Cameras
A brief word about software (monitoring) the Trendnet and Hikvision cameras both come with monitoring software that supports more than one camera and is windows based, it very possible if you are only going to install a few cameras and have a spare windows box to just uses the software that comes with the cameras and forgo everything else I'm telling you with the exception of powering the cameras. There are also other free solutions for monitoring cameras that might be of interest to you..
http://listoffreeware.com/list-of-best-free-cctv-security-surveillance-software/
Back to cameras.....if you require a camera with PTZ (pan, tilt, zoom) capabilities it's going to cost you some serious coin, a good, dependable IP based PTZ camera start in the $500 range ea (take a look at a company call Axis) http://www.axis.com/us/en/ these are the Cadillac of cameras. While there are cheap Chinese PTZ cameras you can buy for around $150 I have tried a couple and have never gotten them to work with Zoneminder. Needless to say it in my case it's better to add more bullet cameras covering different areas than to buy a PTZ although I will probably will add one to one area I want to cover that has street access and would require 3 or more bullet cameras to get the coverage I want. The non-POE IP cameras will require power somewhere close to where the camera is deployed, this in normally accomplished with a low voltage transformer (wall wart) plugged in somewhere and a additional cable ran with the data cable to power the camera, this is a source of vulnerability and failure in these types of cameras, stand-alone analog camera systems are ran and powered the very same way with the exception of using coax cable instead of cat5 for data.
Currently I have 7 cameras up and running and will before the end of the summer add maybe 7 more at $100+ a pop I do it in stages so the cost is being spread out over close to a year, the system works great, you can read on the Zoneminder WiKi about the motion detect, recording, and all the different features. My cameras are all set to motion detect which means you can watch a live stream from each camera and they only record when they detect motion.
Since Zoneminder runs on Apache (as a web site) it can be accessed by any device on your network be it a PC tablet, or phone all that is required is that it have a browser and be on your network, and of course you can open the port and have access from anywhere in the world if you choose to do so.
The other thing I'd stress is this isn't cheap, if you want cheap your going to have to buy junk wireless cameras or a complete stand alone analog camera/dvr solution from somewhere like Sams or Costco. Wireless cameras are fine indoors but outside they are way too easy to defeat, jam, intercept, and are bothered by RFI causing video quality issues.
I'm sure I'm leaving out a lot, but that's enough info to get you started and maybe make a decision, if you have any questions just ask and if I figure out I missed something important I add to this post.