It depends on what IP cams and the format. I personally stay away from MPEG-4 cameras in general since future technology is heading for Motion JPEG. All that said, Axis cameras are probably the best for superior image quality and adaptability. The Trendnet IP-100, IP-300 and IP-400 are pretty good cameras for the price. Usually on NewEgg.com, you can find both cameras. For the Axis Camera, I have found Model #211 to be suitable for Indoor and Outdoor use.
The other reason for Motion Jpeg and IP cameras is the FTP mode and you can ditch the computer. The motion detect built into the listed cameras allows you send video to a server (basically the same way you upload a webpage to a server) for storage.
If you used a computer like you were thinking about for a commercial system, anyone can sabbotage the system by simply unplugging the computer. The IP cameras are basically mini computers.
The other thing is that you must buy a Microsoft XP or OS which cuts into your profit for the computer idea you were wondering about. If you must use a computer(do not buy anything less than a Core2Duo and 2 gig ram to run everything), consider Linux Ubuntu as the OS since it is free. Then go check out Zoneminder.com It allows you so many features and it works flawlessly with the cameras I listed.
Hope this helps. It has taken me literally 6 to 8 months of research and testing alot of cameras, software, writing programs, etc.....
IP cameras are upgradeable technology unlike analog cameras. Think of it as Cellular phone technology. Would you rather have a Analog Brick Motorola phone or a Digital Apple I-phone? 99% of people will want a Digital I-Phone. The 1% other people, well, just walk away from them.