wow that is extremely hot. First thing you should do is shut it off, make sure there is nothing stuck to the harddrive or anything like that. What are the other temps in your case like? Make sure there is no air restriction. If the problem persists, contact the HDD manufacturer.
had HDD faliure last week, lost all my MP3's, opened up the case and found my HDD was extremly hot, like burning almost so thats screwed, hmmm uptime of a week aint good in a confined case :S - M@