We have a Windows 2000 machine connected to our T1 line along with
some other computers.  The Windows 2000 machine has videos cameras
connected to it that can stream pictures real time over the internet,
which we can use to monitor things in our building remotely.

However, when using this software it uses a lot of bandwidth and makes
the other computers very slow.

Is there a way to set a network/ethernet card in Windows 2000 to
send/receive data at a slower rate?

The easiest way to accomplish this is to use 3rd party software to
limit access to the network no a per-application basis.  Netlimiter
(http://www.netlimiter.com/buy.php) should accomplish this.