Hello
There has always been some confusion about what is stated in the guide and release notes about 2003 and 2003 R2.
From a technical point of view - they are both supported. That means there is nothing in Converter code base that prevents them to be used, also the tests have been done with both 2K3 and 2K3R2. (I mean Converter 5.x and 6.0)
I am not quite sure which service packs have been tested but the general approach is that it is recommended to have the latest SP.
In general our guideline is to support all OS versions still supported by the vendor by Converter GA date. (which implies 6.0 still supports 2K3 but expect it to dropped with the next release; and don't regard that as a commitment, exceptions may apply :-).
HTH,
Plamen