But isnt it possible to communicate between director and pd over the tcp protocol? I'm not sure what netsend/receive do, but shouldnt that be possible as well?
Yes you can but i would advise to use Flashserver instead. Far simpler than dealing with the Director Multiuserserver. However, if you are working on Mac OS 9 i would use the OSCar xtra. On Win or OSX you better use Flashserver external
Check this example for communicating Director to PD via flashserver: http://www.ixi-software.net/iua/dir_pd.zip
I am not sure how familiar you are with Lingo but if you have any programming background it shouldn't be difficult to modify this example for your own purposes. Its full with comments and ready for students to modify and reuse.
About video performance in director. i havent really work that much with video. check this out to see whats possible (only Mac OS9 !!). http://www.ixi-software.net/content/download/picker.sit
Its a tool developed by my colleague that uses video and pictures. It gets the rgb values from some points on the screen and sends them out to MAX/MSP and Supercollider using OSC protocole. Those variable numbers can be used to control different aspects of sound structures.
its not what you are looking for (its actually the oposite: control sound from a visual interface) but it mixes video and pictures applying different effects to the video and picts (transparecies, inks, blands, etc...). So you can get an idea if what can be done and how fast it performs
you could also check the macromedia website to see if there is any xtra that allows for more control over video, but i never heard of it.
there is also a tool for real time video manipulation called vvvv or somilar but i don't really know if its any good and i think its only for windows.
hope this helps