Alright I'll back up my program files folders before the upgrade. My OS drive is a small Plextor ssd(60gb) so all my pictures, videos, music, document files ect. are all on secondary HDDs which shouldn't be affected right?
How did you set up your drive so your data was on D? If you are just saving data to D manually in your own folders, then you should be fine. Just make an image of C (you can do this in Windows 7 backup -
http://www.ehow.com/how_5783794_create-windows-backup-image.html). Your program files and data on D shouldn't be lost. But if at all possible, to be on the safe side, you really should do a full backup of the data partition as well.
If you changed the location of your Documents, Downloads, and other user folders by right clicking on them, clicking properties, location, and setting the new target directory location, I would GUESS you'll be fine, but I've never upgraded under these circumstances.
However, if you did anything fancy like using a directory junction to move your Users or ProgramData folders to D (which is what I did when I moved Windows to an SSD but left my data on the HD), I believe the upgrade to 8 will not work. In that situation, you're going to have to move Windows back to the HD first, then upgrade. Also, if you did use junctions, you may not be able to go back to that setup after moving to Windows 8. I have a thread here about it:
http://forums.anandtech.com/showthread.php?t=2280268. If you don't know what junctions are and you didn't have someone else setup your system, ignore this paragraph.