Some good points jaclaz. I did want to challenge a couple of them with my experiences (not to be argumentative at all, but just to provide my own experiences. For running a 64-bit app on a 64-bit OS, I would find it is usually snappier. I am running an experiental x64 build of Seamonkey, and it seems to render slightly more quickly than an x86 build on 32-bit XP. Outlook 2003 (an x86 app) should be slower on WinXP x64 since it's running on WOW emulation. But I wonder if more memory access allows more cache allocation to a 32-bit app (perhaps that may offset the speed dcrease from running in an emulation layer, is that possible?) I have found using PAE mode memory access on Windows Server 2003 creates a noticeable performance hit, compared to accessing more memory with an x64 OS. Just some thoughts.