Is it possible to use a standard USB webcam with the RPi, or is there a specific peripheral that should be used?
I would like to use RPi's to stream images from webcams to the net.
As long as the webcam is Linux compatible it should be possible to get it to work.
However, if there are not ARM specific drivers available, you will have to build them yourself, which is often not easy.
Raspberry Pi Foundation is also planning to make a camera module available at some point in the future. You can see a prototype at: http://www.raspberrypi.org/archives/1254.
This camera will connect via the CSI port - which means it will have the added advantage of not using up a USB port
So in summary, use a linux friendly camera with arm drivers for now - but prepare to upgrade to CSI cameras in future.