You can also set which drive the swap file is located on. It does NOT have to be your system drive. This can free up quite a bit of space.
Right click My Computer, them Properties > Advanced > in the performance category click Settings > Advanced > in the virtual memory category click Change. Click the desired drive, if changing size limitations click Set, then OK.
Reboot. You may need to delete pagefile.sys from its original location. This is almost always a good way to free up space on the System drive.