If you are only showing one camera at a time, I would get a video switcher (something as simple as a 4x1 [
example] will do, or even a cheap $5 "multiple input switcher" for a tv set with RCA-Ins or you can go all out and get a used production switcher (not quite as cheap).
Then, you will need a capture device. I currently use a Dazzle DPM USB (USB 1.1 MPEG stream Encoder, resolution is about 1/2 D1). You can pick up an "Analog TV capture card" with composite input quite cheap right now in the US with the switch to ATSC (DTV), even with full DV or D1 resolution.
For a capture device (card or usb) with proper drivers on Windows (WDM) or Linux (V4L/V4L2), there is a variety of software available to manage a stream or streams.
VLC* is very configurable although it isn't very user friendly for users not acquainted with streaming and IP technologies, Windows Media Encoder is available (for Windows) for free and can create streams and compressed files and is a bit more user-friendly than VLC. Many other options are available (including tools designed for webcams that post a jpeg image each minute and set the page to refresh for viewers), but these options listed (along with a websearch) should get you started.
Let us know if there's anything more you want input on
* I am a bit biased, I mean, my name is [finally] in the thanks file ![Wink ;)](./images/smilies/icon_wink.gif)