Even though the original post

The original post here was made in 2009, so a lot has changed since then.

One of the easiest and cheapest ways to run multiple web cams is to purchase Manycam software. Depending on how many cams you need, it can handle up to twelve webcams. You’d need a PC with USB 3.0 and a 3.0 hub but the cost is reasonable. To run several cameras would require a well-spec’d PC to handle that type of load. Having used it myself for two cams, I can say it works well. Has some cool effects and transitions too.

http://www.manycam.com