Partitioned tables with striping for performance?

I'm trying to understand partitioning's positive impact on performance. I understand that a partitioned table can allow Oracle to cut down on the amount of disk it might have to scan based on the where criterion of the query. What I don't understand is if a disk array is striped, how does partitioning help in performance.

-- 
Galen Boyer
It seems to me, I remember every single thing I know.