From what i can gather, sounds to me like the tech. has installed one 'physical' Hdd that has been patitioned into two sections. These 2 partitions being termed, local disk C: and local disk I:
Also sounds as though your windows operating system, program directory etc have been retained on c: so keep it that way.
While keeping all your system operational files on c:, the logical thing to do would be to keep all your important documents ie. music, photo's, video's (including all your downloads) etc on patition I:
Access local disk I: through 'my computer' and set yourself up suitable filing system, with folders that display what you keep.
Then its simply a matter of 'moving ' the important documents that remain on c: into the relevent folders you have created in I:
You need to re-direct your downloads to the folders on I: by accessing tools>options>folders (or similar) at the host sites your D/L from!
cheers.....