Rapidly Running Out Room On C Drive

I've recently purchased a Toshiba P200D-139, which came with Vista pre-installed. The HDD has come partitioned in C (Vista) and E (Data). TBH, I want just 1 drive. I???ve used the disk management function in Vista, and I???ve even done it manually in the cmd prompt, however I cannot extend the C drive at all. I can erase E, I can split it, I can create new drives, extend them, shrink them or whatever, either through the disk management function, or through diskpart.exe in the cmd prompt. I can do anything and everything to the E drive.

However the extend options for the C drive are greyed out. In the cmd prompt if you try to extend the C drive it says there???s insufficient space, yet if you try with the E drive it works fine. Does anyone have any ideas? I'm rapidly running out of room on the C drive, and don't see the point of splitting the same type of data across 2 partitions, espeically when a lot of it is shared/public.