When you install windows there is no C partition or any other letter for that matter. They are only labeled after windows is installed. The way you know which is which during an install is by there size. As long as you know which partition you want to install windows on you will be fine, and as long as you only format that partition and install windows on it, your other partition will not be affected and your files will be fine.
1 other important thing, if you have files that need a program to access them, that program will have to be installed on your new windows 7 install. Such as a word document or a pdf, you will have to install Microsoft Office Word and Adobe Reader etc.
Clean Install Windows 7