I'm going through this with my notebook -- the hard drive occasionally makes very bad noises, and I've had a number of read/write errors, too. It hasn't actually crashed yet, but I'm assuming it won't be long.
I was going to buy an exact replacement from Dell, but I found some better deals at Provantage.
They had the exact replacement drive for my laptop, but I ended up buying a larger capacity, faster drive for less money. I'll have to do some messing around to get my data on to this new drive, but the extra capacity will be nice.