you dont want to do that as the data drive is used for another purpose, not storage for your use.
it should be kinda small and contain the recovery insof for vista. if you try to use it, it will fill up faster than what you're doing now.
could be wrong but need more info for a better answer.
ok then. this is likely how it was set up for some reason, but you will either need to 'span' drives in managment so that it does what you ask, which will reconfigure drives to dynamic partitions, or you need to tell windows to use it in places like 'my documents' and it iwll ask you if you want to move the entie contents of the folder there....
be very sure/careful here.
teh easeus partition program works well, but one of hte main reasons for seperating a data parition is so you can do a system recovery w/o having to back up data or worry about losing it. i actually use a seperate drive for data/music/dvds/etc.