Don't use camstudio, that and camtasia usually suck majorly.
As for Windows movie maker there is a zoom in effect, but i don't think there are any options to how far it will actually zoom. if only Hitman were here...
Edit: I was talking about "Ease in" you can't change it around at all, oh and don't worry about the quality of the preview, it is much better when it is all finished.