It means your sytem was supplied with a single disk, with two partitions (local disks) and win is installed on C and little if anything on D
You can move your Librarys (data files) to another location (eg D)
http://www.sevenforums.com/tutorials/18629-user-folders-change-default-location.html
And when you install a program you can custom install and select a new location.
Or you can merge the two partitions so everything is on C (A better option in my opinion) but you would need a third party tool to do so (and backup your data first) eg Acronis Disk Director, to name one such tool
BTW only QB 2010 or later is win7 compatible