Let users link webcams in website to stream

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You will need to use rtmp / rtsp server for this scenario. There are several rtsp server available.

Red5 http://osflash.org/red5
Wowza http://www.wowzamedia.com/
WebOrb http://www.themidnightcoders.com/products.html
ErlyVideo http://erlyvideo.org/
RubyIzumi http://code.google.com/p/rubyizumi/
RTMPD http://www.rtmpd.com/
Cygnal http://wiki.gnashdev.org/Cygnal
RTMPy http://rtmpy.org/wiki/RTMP
RTMPlite http://code.google.com/p/rtmplite/
MammothServer (OpenFMS) http://mammothserver.org/

In my opinion Wowza and Red5 will solve your problem.