Just sent you 2 screenshots, one of the 64-bit dxdiag gui output and the System Properties, showing 64 bit mode... I will do, just for completeness sake, a 32-bit Vista Playback.exe run on a 1920x1080 screen.
(As I said in Reply #7: I had not specifically tested hi-res on 32-bit, or could not remember having issues there...)
UPDATE: Yes, Playback.exe runs fine on 32-bit (Vista and W7) on 1920x1080, but with a lot of black around (sides mostly) the 1280x1024 app-image, but none of the 64-bit boys allow for anything above 1280x1024.
I did not want to lug around my 1920x1200 screen to check on other boxes, so that's why only 1920x1080...