This I assume is a reasonably basic question; I know the basics of Sony Vegas, but certainly not a pro.
I stuck and have been searching for an answer, but must be using the wrong search terms and can't find what I am looking for.

I have converted all my powerpoint slides to images and will insert them across the top timeline

I have done green screen before and managed that ok, but what I want to do this time is 'shrink' my talking head down so it only appears in the bottom right of the powerpoint image.

Do i have to record my talking head in the bottom right of the video recording or can I record myself full screen and is there a way to shrink it down in Sony Vegas and move it to show in the bottom right if the powerpoint image?

Any pointers in the right direction will be appreciated.