Today I've received a PS3 Eye cam. I've chosen this webcam because I need a good image quality and a high frame rate. Thanks to AlexP on the NUI Group's forum (you can find the topic here), a driver is available to use the PS3 cam with a computer. So far it can't be use in an other program but I hope it'll be available soon.
I keep my Logitech QuickCam Messenger (I think it's its name ???) to develop the software. So far every part works. I cap in 320x240 @ 30 FPS and it's fluent once blobs are displayed with opengl. However the image of the hands isn't displayed at the same time (I have only one webcam working) so I hope that having to process 2 webcam at the same time won't be a problem (I use a notebook with 1GB of RAM cadenced at 2,16 GHz (core duo)).
My next steps are to make Otira faster. Apparently I use a slow opencv function to get pixels' values ( I use the "Indirect access method" : http://www.cs.iit.edu/~agam/cs512/lect-notes/opencv-intro/index.html). The stability of the captured image is to be improved to. The coming tough part is the opengl side of the project. I'm not really good at making efficient UI. If someone knows a good UI, send me a message ;-)