I would say partition it. Obviously the best time to partition is before the install of the Os but if not used the most upto date version of partition magic you can find. The only time i had any real problems with repartitioning an active disk is when i used an old version of PM on a windows 2000 disk just when it was released.
Follow Nihils recommendations and you should be ok. I know i have been saved hours of work because of having partitioned a disk in the past.