You have posted this in the VisionLab forum, though your profile indicates that you only own EffectsLab. Which of these programs are you using? It makes a huge difference.
In VisionLab, you can use pretty much any technique you want to. Split screen, greenscreen, bluescreen, hand-drawn masks, etc.
In Effectslab, things will be much more difficult, since its not even supposed to be able to do that kind of compositing. There is a way though, and it involves using split screen. Tutorial