|First move over all of your files including documents, music, video, etc.|
Second, find all of your programs that you have the install medium for. Go to add-remove programs and uninstall all of those programs that you can reinstall without too much trouble. Also uninstall programs you no longer use, or programs that came with your computer that you never use. Reinstall one at a time, selecting the custom option and pointing the installer to the larger drive
Third, do a disk clean up, and then a defrag.
See how much space you now have. If it is still on the low side, you should look into two other things: System restore - see how much drive space is dedicated to system restore, if it is a little high, reducing this % space will clean out older restore points, leaving just newer ones. Then look into virtual memory, if it is a little high, try reducing the amount to equal to your RAM on the main drive, and adding about the same amount as auxiliary on the second drive. The defrag again.