There are three things to figure out:
1.) Framing. You will want to frame each shot, so that there is room for both shots.
2.) Using PiP to get the Video from two Clips into the same shot.
3.) Green screen shooting to eliminate the background, unless your framing above is perfect.
PrE 8 has Video Merge to help with this, but I have not used it. I shoot greenscreen, but use a Keying module in Adobe AfterEffects to separate my subject from the background.
Good luck, and maybe a user with experience in PrE's Video Merge can comment. It might be very useful and solve some of the problems.
Thanks for the help. I will defiantly let you know if it works.
It looks like you replied via your e-mail's POP server. You signature shows, and contains personal info. You might want to delete that. The forum is open, and it's not a good idea to have such info, as one never knows who is reading. I replied to my reply, so that you should still have access to the post. Had I replied to your reply, you would loose the editing capability. I'll also alert the MOD's, so that they can remove it, should you not see this soon.
Good luck with the project,