Is ECC 6.0 supported on Windows 2003 Server 64bit?

Check ControlCenter 6.0 Support Matrix document - http://powerlink.emc.com/km/live1/en_US/Offering_Technical/Interoperability_Matrix/DocLib/300-004-026_a16_elccnt_0.pdf?mtcs=ZXZlbnRUeXBlPUttQ2xpY2tDb250ZW50RXZlbnQsZG9jdW1lbnRJZD0wOTAxNDA2NjgwMzIxZWUwLA__
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Supported 64-bit Windows 2003 are: Windows Server 2003 x64 (includes SP1), SP2, R2 (Standard, Enterprise, Datacenter Editions).

It is supported and we have been running ECC 6.0 on Windows 2003 64-bit addition from the start. We've had a number of software related issues with ECC, but none were related to running the 64-bit vs 32-bit versions of Windows.

So in short - seems to work like a champ. Just make sure you get the most up-to-date ECC 6.0 patches applied with your installation and you should be fine.