From someone name Eyal: It is somewhat of an ugly kludge but I managed to find out why SPSS determines that Vista was an NT Terminal Server (while XP is not) - it does so by checking a registry entry under HKLM\SYSTEM\CurrentControlSet\Control\ProductOptions (one that simply reads “Terminal Server”, btw).
By making sure your user doesn’t have permission to read the entry the problem is circumvented (I checked ‘Deny read permission’ for my specific userid on the key).
Note that you will need to do that on a permanent basis (SPSS checks that key whenever it is started) - I do not think this will have any harmful effects, but if it does you can always undo it and create an SPSS user.

I haven’t tried it yet, but will do so. It is an SPSS incompatibility problem. I don’t feel like shelling out more for software than I paid for a hardware and an OS. I’ll see if it works or I’ll run XP in a virtual environment and install it there.