007 is correct about Ctrl to expand the clip, but the only snag is you are limited to one speed.You can speed up, slow down and even halt a scene using the Velocity Envelope tool. We went into great detail about that on this thread...
http://www.videoforums.co.uk/sony-vegas-media-studio/9945-how-do-velocity-slow-motion-effect.html and I posted a couple of clips there demonstrating what can be achieved.
Also, I got the impression from your post that you want to actually take someone or something from one clip and move it to another... If that is so, you would be better using Track Motion and masking rather than Pan Crop. It'll be a fiddly job but can be done. About halfway through this clip
http://www.turnmedia.co.uk/videos/lib.wmv I cut the beatles out of the Sgt Pepper cover, and had them move forward while the rest blurs. That was done with masking and track motion.