How can I stop Windows 7 putting all my data onto C drive?

The person who built my computer put a partition in my hard drive (I didn't ask him to). Trying to make the best of it, I decided to store all my data on D Drive, however, Windows 7 automatically puts everything onto C drive: downloads, Library, etc.

This makes it so confusing and it is annoying to have to search through complex folder trees to find anything. It also defeats the purpose of using C to hold only programs and system files, and D for data storage.

I recently lost half my pictures (more than 5,000) trying to sort them out and put them in one place.

I'm sure there must be a way to set up the drives that allows what I want to do without all the complications. Right?