Title says it. I ran my own tests (ugh)
Hardware:
C2D E6600 at 3.4 g
4 megs OCZ Platinum at 4-4-4-12, 1 to 1
All setups are a clean install with the latest patches and service packs and a clean install of Adobe Production Studio Pro CS2

Ran 4 tests each setup. Rendered in Adobe Premier Pro CS2 to file a 4 minute video with some basic titles, transitions and effects created in After Effects 7 and stereo audio.
Average run times:
XP Pro: 4:32
XP 64 Pro: 4:54
Vista 32 Ultimate: 6:18
Vista 64 Ultimate: 6:31
Did not want to event try a 1 to 2 hour video.... got to sleep some time.