Well, for the short term, you can. I've performed that a few times with XP, and once with 2000. Just used XP setup to make partitions, then find one that works. Of course, you then have less space for Windows to run on.
But at some point the HD will likely fail - the longest they've run for me was about 2 months, after doing that. So it's probably better to just replace the HD, rather than take your chances, if you've got a machine (and data) you care about.