You don't need to re-partition your hard disk again. Partitions are OS-independent. You can install Windows 8 over Windows 7 in C: drive.
If you're performing normal upgrade (with default option),. Even your installed applications will be preserved. Means, you'll find your existing compatible applications installed when you'll boot Windows 8.
If you're doing fresh upgrade/install, you'll find fresh default Windows 8 without any third-party software installed. You can find Users etc folder created by previous OS in
C:\Windows.old folder. And, other folders of C: drive would be intact.
So, in any case, you won't loose your files from even C: drive, loosing data from other drive is a remote thing.
Warning: With the installation from boot media, if you choose to format C: drive, you'll loose data from C: drive. Formating C: drive isn't mandatory.