The belts on a Dyson 04 I dont think were ever designed to be replaced by the man in the street but with patience an basic skills it can be done. It is advised to replace both belts at the same time.
Special Tools required:
1 Long bladed T15 screwdriver
1 T10 screwdriver
and an external circlip pliers.
1 Remove sole plate assembly
2 Remove brush
3 Remove Brush housing assembly this is a little tricky with machine upside down and motor towards you tilt the brush housing assembly towards you gently pull out from side furthest from clutch and then the other side. Disconnect from pipe.
4 Using T15 screwdriver remove 3 screws from clutch cover 1 can only be found by positioning head of cleaner in upright position and sliding screwdriver thro hole in motor cover.
5 Prize off yellow control knob and then with a bit of gentle persuasion the clutch will come out.
6 Remove 2 T10 screws from metal end cover which will give access to primary drive belt.
7 Using circlip pliers remove circlip from drive shaft at other end and pull out drive shaft gentle feeding final drive belt off.
Rebuild is a reversal of the strip down.
Hope this helps.
Doug
December 2007