Well, I would have a look at the latest SP of 3.1 then. If you want to confirm Win 2008 compatability you should look at the Product Availability Matrix (PAM) on the SAP site.
Post on releases on BO here:-
https://bobj-board.org/t/212450
When you say compatable with XIr2, there have been Webi calculation engine changes since that release and 3.1.
You will find that reports will require a fair amount of variable re-work, depending on the complexity of your reports.
Mak 1 
(BOB member since 2005-01-06)