Dimension 8300

I have a dimension 8300 with a pentium 4. A couple years ago my hard drive corrupted windows and I had to get another. The original drive wasn't lost so I slaved it (well my roommate did for me). It is going on 7 years old, I don't want to replace it because I don't do all that much computing other than Internet, shopping, email. I was thinking of backing up all my important files; music, photos, emails, a few programs, and just wiping the primary drive, then reinstalling windows, other programs, etc; and wiping the slave as well. It has just seriously slowed down over the years and this seems to be the only realistic option other than buying a shiny new one which I don't need. Any ideas?