If you are using Vegas Movie Studio - you can have up to 4 video tracks. Pan crop should do what you want. If you need to overlay a video now you are talking composite. It might be easier to find out more if you click on the search just above and to the right - next to forums - and use the key search word "composite". There are a bunch of pretty detailed examples written by several people. Also think about constructin your video in stages. Use a grid to lay out the first stage - render that to a seperate file. Then drop it back into the software for a second pass.

I am not familiar with movie maker 6 - if that is the software you are using you may be in the wrong forum - unless that is one of the older Sony products - perhaps one of the veterans can help you there - you may want to use that in the subject line.

good luck with it