Okay, Like2Edit, you can put nothing into Layer 1, if you like. In that case, it'll be black. Or you can put a color matte there. A color matte (and I'm trying to retrieve this data from memory, so I might be a bit off) is at Project >> New >> Color Matte and it lets you just make a solid color and place on the timeline. Basically, if you want a purple background, you can do that.
A motion background would be, like, you making just some groovy miasmic moving pattern. Something that loops smoothly. Then you put it on the background (Video 1). That way, if you squash your video in a certain way, it's bordered by the background image (which can be whatever you like) instead of Premiere's default (which is black).
Now, as I re-read what you wrote, I'm no longer sure if you want to squash the two screens apart (for example, the way they screw with credits on network TV by squeezing the credits over while an ad runs on another part of the screen, which I think is reprehensible at best) or if you want to split 'em down the middle (for example, Clip 46 has Joe talking on the phone, and he's on the right side of the screen. Clip 47 has Linda talking on the phone to Joe and she's on the left side of the screen and you want to show them both).
I gave you directions for squashing (which doesn't necessarily have to involve messing with the aspect ratios -- for example, the opening sequence to The Brady Bunch), and the directions for splitting a screen is a different thing.
Bytemaster34's directions are pretty much the thing you'll need for that.
There are a couple of other hacks to achieve the same effect, so if these don't work, post more specific details and one of us will probably come up with something that smells good and tastes great, too!
Cheers,
![[monkey] [monkey] [monkey]](/data/assets/smilies/monkey.gif)
Edward
"Cut a hole in the door. Hang a flap. Criminy, why didn't I think of this earlier?!" -- inventor of the cat door