According to this How-To Geek blog post (http://www.howtogeek.com/howto/windows-vista/resize-a-partition-for-free-in-windows-vista/), Windows Vista and more recent versions of Windows have the option to manipulate partitions. In particular, it can resize and expand.
I have a computer with a 100GB C drive and 350GB D drive with C drive constantly running out of space. Trying out the windows option suggested by How-To Geek, I find that the resize option is not useful because resizing the D drives unallocate space at the *end* of the D partition. Because there doesn't seem to have an option to move the partition, I still cannot expand the C drive to take up the unallocated space.
I gave up the windows option and use Paragon's free partition manager instead (http://www.paragon-software.com/home/pm-express/download.html). The program doesn't have all that many options, but at least it can *move* partitions.