If its an all floors model, as mine is you need to remove the cover and brush, then remove the bottom hose. Unclip the plastic piece which the brush was in.
Then you see a black plastic cover where the belt either was or still is. this has three torx screws in (Tx15)two at the front one very deep at the rear.
once this is removed, My 'all floors' model has a knob for switching the brush on and off, prize this off with a screwdriver,then lever the clutch assembly up whilst pulling forward away from the machine, it's a tight fit but just pops out.
I have done this on mine as the clutch to brush belt has snapped, then I dissassembled the clutch itself and searched the net for a new belt, only to find that the belt isnt available on its own! Maybe Dyson feel we aren't capable of doing this procedure?
So as a result I now have to buy the whole clutch assembly with belt already on!
Instead of £3-£5 I now have to spend £16-£20 just for a belt!
Oh well Its a damn good Vacuum cleaner so I suppose I'll be paying it :-P
Fredd Raistrick, February 2008