Free video compositing software help

[thebluebus]

I currently only use free software for playing with videos.

Because I'm not buying anything good until I've got a nice new computer to put it on.

So I need help.

I want to be able to make a picture-in-picture effect in a video I'm doing.



For example.

I have a video clip of a poor Jennifer Aniston lookalike, thus -




And also a smashing clip of Moss from the IT Crowd, like this -




I want to crop them down and composite the two together to give me a video like this -



See?

Help please!


ps. apologies if this should be in Photography & Video.

[thebluebus]

I should have said, for Windows.