Hi Ian,
actually, XP64 is the only Windows system that is not officially supported - although it works, we will not actively support and develop for it in the future.
Here´s how it works: If you use VE PRO 32 bit, you can access up to 2.8 GB of RAM all in all - all VE PRO instances connect to 1 VE PRO Server.
If you use VE PRO 64 bit with Vienna Instruments, Vienna Imperial and other 64 bit plug-ins, you can load as much RAM as you have available [:)]
And of course you can run 32- and 64 bit instances simultaneously.
Best,
Paul