partitioning a hard drive slows it down, not speed it up. It makes no sense to do this at all with hard drives very cheap, if you reinstall windows alot then just pick up seperate harddrive.
As far as hard drives failing, it's pretty rare but does happen. Premature failure can be related to poor quality of drive, handling before you got it or you bang it around / drop it etc, heat in the machine, or use.
If you keep heat in check, it should last a good long time. Get one with a 5yr warranty, that typically signifies quality... no company is going to warranty something for that long if they aren't sure whether it will last that long or not. This however doesn't mean you won't suffer a failure. but if you keep heat to a minimum / handle with care your chances are pretty good.