I experienced a shortage of free space on drive C after installing Windows 7 SP 1. To overcome this problem, I change the size of the D drive partition and then added to drive C. To do this I need a partition manager software. Software that I use is MiniTool Partition Wizard Home Edition which is a free software (freeware).
Its use is very easy. you just need to pull a slider that exists and leave the rest to this freeware.
First, do the resize on the D drive (see first picture, pull the bar to the right). From this process there will be an empty space (unallocated) between drives C and D.
Second, combine the blank space (second picture) to drive C by pulling the lever such as resize drive D. Process will start automatically by doing a few times restart the system.
Now, my Seven already integrated with SP1 and other updates and still have enough free space.
Interested in trying or using this software? Please direct them to the official website.