I have 2 hard drives with  8 partitions between them. A 40gb with 6 partitions and a 120Gb with 2.
  C:\  8 Gb
        My current windows xp install, a slipstreamed SP2 RC2
  D:\ (Media) 10Gb
        It used to be home to audio video and pictures but my audio folder has
        grown a lot recently so now it just my ripped CDs and a folder of
        "drmed napster stuff" which I have downloaded but not paid for. I keep
        it seperate becuase I can't listen to it on other machines or synchronise
        it with my mp3 player. It also has midi files and soundfonts.
  E:\ (Games) 10Gb
        Games are getting so big now that I only have room for a few at a time.
        It contains Jedi Knight 2, Tron 2.0, The Singles, Half Life, Elite Force
        2, and various other demos.
 F:\  5Gb
      A previous windows install. SP2 RC1 I think. Got kinda crowded in
      there so I decided to go back to using C:
G:\  (Programming)  1Gb
        Where I keep all my source code and some SDKs. Oh and a game
        crept in there somehow, Elite Force 1.
H:\ (Longhorn)  5Gb
       Just an install of build 4074
K:\ (Huge) 80Gb
        Mostly a scratch drive for stuff I record off the TV with my digital TV  
        card. It comes in at about 1Gb an hour so I can use it up pretty fast
        especially since I havn't got around to putting the stuff onto DVDR yet.
L:\ (Backup) 35Gb
       General mishmash of stuff I want to keep. Downloaded programs, iso
        images, virtual pc images, ebooks, videos, etc.

It's not as organised as I would like, but it helps me start looking in the right general direction. I recently installed Picassa and let it do a search across all the partitions and was very surprised how many pictures it found that I had completely forgotten I had.