|For about $40.00 US you can purchase a second hard drive around 500GB and move all or most of your personal files over to the new drive, leaving more room for your operating system and programs.|
As a TEMPORARY solution, you can reduce the space that system restore uses from 15% to 18% down to 10% to 12% and the only thing you will loose is a few of your older restore points. This will gain you at least a few additional GB of space which will make your system run more stable, but you will ultimately need to add more space and a second drive is the best way.
You have to be a little bit crazy to keep you from going insane.
If all else fails, read instructions.