How to render only the shadows of a scene's geometry without seeing the geometry?

[CutMasterClaw]

hello everybody, hopefully someone out there can provide some help concerning my problem. I have to use the alpha compositor technique to combine two different views of a scene in order to preserve rendering time. it's a race track and my problem is concerning the first-person-view of the pilot. first i do render the track itself, then i put the inner cockpit view seen through the cockpit's windows over the track view using the alpha compositor. in the inner cockpit view i need now only the shadows to be thrown at the cockpits geometry but the geometry of the scene (everything outside the cockpit, the whole track) shall not be seen.
i hope it's clear what my problem is. thanx for any help in advance.

[DeadlyFreeze]

If you right click on an object in your viewport and go to properties you can turn off an objects visibility with 'visable to camera'.

[pheonex]

what about the "matte/shadow" material??? can you use that?

[goat]

pheonex had it right. make everything outside the cockpit a matte shadow. Save as a png,tga the composite them witht the outside render. should work fine.