- create a strip-like black rectangle in PrPro Titler and align it appropriately;
- place two copies of this title on top of all your video tracks one above the other;
- with the Position property of the Motion effect move upper rectangle above the top of the screen and lower rectangle below the screen;
- animate Position property of both rectangles so that they 'meet', splitting your screen into two parts.
No sweat. Just multiple steps.
Start with animating the lines coming up and down to separate the screen. You can use the titler in Premiere Pro to create two titles. One line in each title so you can animate them easier.
At the exact moment when the lines touch, you are now using Picture in Picture. In fact, it might be easier to use Picture In Picture to begin with, but so well cropped that it isn't even noticeable. Then when the lines come together, you zoom in a little on both tracks to achieve that look. Zooming in normally loses quality, but if you were shooting 1080 and editing in a 720 sequence, then you could be zooming back to 100% instead of zooming in past that.
There are other ways, and it is probably easier to use After Effects for shots like this, it can be done in Premiere Pro with a little work.
Oh my God that turned out AWESOME, thank you so much the both of you for your help!
It wasn't hard to do at all in premiere :S I can only imagine how easy it is in AE.