Willem, the forum of kdenlive (at http://www.kdenlive.org
) is a better place to ask for kdenlive specific help.
A couple of notes:
which version of kdenlive are you using at this moment?
Are all necessary dependencies installed?
Have you cheked your default project settings?
Is the cam being recognised, in other words are you able to capture anything at all upon pressing the record button?
I haven't worked much with kdenlive lately (yes I am waiting for an up and running 0.7 version), but you can PM me, or check my postings in the dutch forum.
All still in 0.x phase, IMO kdenlive remains a very promising video editor for linux