what version of Processing are you using?

I think it is 1.5.1 version.

you didn't mention what OS you're working on.

if its windows...
on XP i had no problems running multiple webcams (tried it with 3) of the same manufacturer.
the cams were listet in the devicemanager with different indices at the end, so the names were unique (at least i think this is the reason).

on win7 (or was it vista, i cant remember) it didn work, because the device manager listet them all with the same name. it seems that the key to this lies in the registry, but i couldnt figure out how to solve this (tried changing the entries in the registry for each cam, but no success).

Processing 2.0a4 comes with a new video library that might behave differently in this regard. Did you give it a try?

Yep, I've just tried it, it looks still same...