Large capacity drives are dirt cheap these days. Buy a new large drive and install it as a second drive in your PC.
Get one of the drive imaging programs like AlohaBobs and move everything on your old drive to the new one. Designate the new drive with the letter you formerly had for the old one and toss out the old one.

With Gigabit drives, it doesn't really pay to spend a lot of time purging unneeded files anymore. However, it does pay to defragment the drive from time to time. I usually keep my old drive installed for a few weeks just to be sure there are no problems, but seldom have to go back to it.