What exactly does "preview monitor" refer to? Premiere does not have a panel by that name. Do you mean Source Monitor? Program Monitor?
Also, what do you mean when you say it "plays back in HD"?
By the way, maybe just a typo in your post, but if you plan to export at 960x450, you may be asking for trouble with those dimensions. It's generally a good idea for the height and width to be evenly divisible by 8. Also, 960x450 is not half of 1920x1080. That would be 960x540.
