Modifying partitions is "hairy" in my opinion. Installing Vista along with XP can cause problems, so I would move the data off the "separate drive", go to Disk Management and delete the whole partition, then make a new partition and format it.
You have done some "no-no's" from my point of view (making Vista partitions and "trying" spanning). I suggest trying to start from scratch by removing the partition on the "separate" drive (that might include low level [zero] formatting).
ALTHOUGH...the error message relates to the registry (without the registry or even if there is major damage in the registry, Windows will not work). What is all the information in the error message? Does it show a program that is generating the message in the top left-hand corner of the error box?
Install and uninstall the Creative program again. Watch that there are no problems.
Try to isolate what is generating the error message, if so, why is it doing it?
PS: Try Event Viewer. (If you don't know where to find Event Viewer, search in Help and Support.)