Hi I've taken a 1080p screen recording on my desktop but only want a specific crop of the actual recorded screen in the final video. How can I do this in Premiere Pro CS4?
You want to use an effect that's called a 4 point garbage matte. It allows you to set 4 points which create a box and everything outside it is removed. Here is a link to a tutorial on how to use the effect 4 point garbage matte.