combine 2 vids together?

[Bilbofett]

whats a good, short+sweet fast program to overlay/merge 2 (or more) vids together, like a melding, interwoven, combining both images into 1 (not append or stack!). I know Premiere can do it, but I have to setup a whole new project just to do that, or edit a timeline, its a bit much. Any other programs to do it, respect the colorspaces, not degrade the video quality, fast?

[zoidberg]

I would say avisynth, but if you've not used it before there's a steep learning curve