The fine folks over at VIAArena have put together an article that that outlines their experiences using the new Windows XP x64 Edition OS.
After installing Avast I transferred my emails that I had saved from my previous system, into Microsoft Outlook Express. Microsoft Outlook Express comes bundled with WinXP x64. I always run spell check before I send an email. But as soon as I hit spell check, I received an error message… Error. Spell Check could not run. I then did a bit of research around the web so to see if this was a common problem under WinXP x64. It seems that Microsoft in their wisdom bundled an email program with WinXP x64 that is itself a 64 bit program, aside from the spell checker. The spell checker does not work at all because Microsoft have not developed a 64 bit spell checker. The 32 bit spell checker used in all Microsoft Office 32 bit applications does work under Win XP x64, except the 64 bit Microsoft Outlook Express. This I found out is a known issue.