I agree; it sounds like the HD may be on its way out.
Break out the Mac OS X install disc 1 that came with your computer, pop it in while the computer is running, then restart the machine and hold down the D key as it's booting. This will bring up the Apple Hardware Test. Run an Extended Test and see what you get reported back to you. Make note of any errors you get--if nothing else, it'll save you the trouble of running through the whole process while you're on the phone with Apple or at the Genius Bar.
Here's hoping for a speedy recovery for your MBP. 😀
~Kalmia