Well, how about opening a terminal under android (terminal emulator by jack pavelich should be fine) and typing "mount" for checking mount points.
Then you could mount the partitions (e.g. "mount -o remount,rw /dev/sda2 /Volumes/useless)
---> This would mount the partition "sda2" as read-write on "/Volumes/useless/" in your android root directory.
Then delete all files on that dir. And google somewhat for further information on how to delete partitions.
Hope this helps.