Yeah, back it up sooner than later (burn to DVD, USB drive, etc). If you got the time you'll get a better price from an online store for a new drive as opposed to a brick and mortar store. I'm guessing it's an IDE drive right? Something like this maybe:
http://www.newegg.com/Product/Product.a ... 6822148104
You can also check your drive manufacturer page to see if they have any downloadable utilities to "diagnose" the drive (something like this:
http://support.wdc.com/download/index.a ... d=3&swid=2) if you want to know for sure.