Ask the Performance Team : WS2008: Upgrade Paths, Resource Limits & Registry Values:
However, cross-platform upgrades (x86 to x64 or vice-versa) are not supported.
Let me restate this table another way for the SBS crowd …..
If you are currently running SBS 2003 (RTM, SP1, R2 or SP2)
You CANNOT inplace upgrade to
SBS next version.
There will be a migration path from 32bit to 64bit. The reason that we have to migrate and cannot inplace is that Exchange 2007 is running 64bit only and that’s why the 64bit requirement is needed.
P.S. You know how you can’t go from XP 32bit to XP 64bit without wiping and starting over? The same rules apply here. It’s a different file structure. SBS 2003 is 32bit. SBS next is 64bit only. Thus there’s a barrier and one cannot do an inplace upgrade. Bottom line it has to be a clean install. http://en.wikipedia.org/wiki/64-bit But don’t panic, there will be a roadmap. And in fact we’ll be better off as inplace upgrades leave behind legacy permission issues. But just get your mind in the mindset that there’s no implace in our future.