I posted the the download link to the vmware appliance in the updated thread here: http://www.howtoforge.com/forums/showthread.php?t=13173
I think he said there will be a way to dump everything from 2.x and upload to 3.x I doubt it'll be a straight update though. You'll probably need a clean install.
What cluster?Active/Active, Active/Passive, how many members (possible). But anyway they won't share the hardware, except you have the cluster across two or more virtual servers in one hw. Especially with such CPs it will break your neck when trying to have a active/active cluster over all services...
The system requirements and configuration for 2.x and 3.x are very different, so there will be no direct update. My idea is to add some kind of data export feature in XML format to ISPConfig 2 to export all account data and add a import whizard to ISPConfig 3. This feature might be used later to import data from other controlpanels to ISPConfig 3 too.