No x64 for you! (on Exchange 2003 that is)

A whole slew of clients has been asking me about this one, so let me set the record straight.  Exchange 2003 will *not* run on x64 OS's.  For those who do not believe me:

MSFT TechNet article on Supported OS for Exchange 2003

Which spells out:

"Note: Exchange Server 2003 does not run on 64-bit editions of Windows Server 2003."

So what does this mean?

1 - You CAN install Exchange 2003 on x64 hardware, just not on the x64 editions of Windows

2 - You CANNOT do an in-place upgrade to 2007, since that needs x64 to run in production environments

So, while you can buy new hardware safely and continue to install and run Exchange 2003 properly with an x86 OS, you can't leverage the 64-bit framework. 

Also, you can't run 2003 on Server 2008 - at least not yet.  This means that the advanced clustering and other 2008 features are not available for Exchange 2003.  It also means that if you buy a new server and get an OEM version of Windows, you will have to specify that you need Windows 2003 x86, otherwise they'll send it with 2008.

Sorry to deflate everyone's balloons at once, but hopefully this will help a few bets pay out between Exchange techies.