If your DC04 has a clutch unit there are two belts. One is the motor>clutch drive belt, the other is the clutch>brushbar belt. The motor belt is available separately, and in theory replaceable. The other belt is assembled together with the clutch into one assembly. It's available from eg. 'eSpares' for around £20. Good luck getting the clutch unit out of the head casing. I can't fathom it!
AndyH, February 2009