Depending on the operating system you use this can be very easy. I originally did this with vista simply by moving all my stuff to a different hard drive, naming it whatever (like Music, Documents, Videos etc.) and then I would right click a my documents link like in the start menu click properties and click the location tab. You can then click move and select the new folder on another drive. If my OS drive goes bad all I lose is well... programs which I need to reinstall no matter what. Unless of course you get really board and back up your registry and everything.
Basically, if you have Vista or Windows 7 what you want is easy, if you have XP... use the guy aboves methods and links.