Well, before doing any more experimenting, I would do a serious backup. If the hard drive is generating heat, there is (as you say) a large chance of something being wrong with it. Because of the chance of it dying at anytime, you won't regret having spared the few CDs it takes to save your important documents, images, internet bookmarks, etc.
You can investigate by purchasing a new drive at a place you know won't give you trouble about returning it if it turns out to be something like the IDE controller. As well, there are hard drive fans that you can get. Even if there isn't such a problem, cooled drives supposedly last much longer and are less prone to dying.
edit: I did a search on hard drive cooling...look at this one: http://startech.com/ststore/ItemList...ar=topbara.htm