Remove the top (3 screws) then take out all screws around the edge of the back panel. Undo electrical connector that joins to heater assembly AS rear panel lifts out. Retrieve broken belt. Make a sketch of how the belt tensioner on the motor sits, as it may fall off if you tip the machine backwards without a belt in place..
Now do yourself a BIG favour, and hoover / brush ALL the dust and fluff out of ALL the ducting in the machine. Pull the front panel out to get to it all. You'll need to have removed the two main bits going across the rear and front to rear to get the new belt in so you might as well. Unless you are very timid, put the drum / rear cover face down on the floor, take the nut in the centre of the rear cover out and remove all the screws that hold the two halves of the heater housing together. Lift the rear cover off the drum, prise the two parts of the heater housing apart (stuck together with a gasket that gets sticky with age but is reuseable). Clean out ALL the fluff before it causes a fire, but don't be violent to the heater element. best to take that bit outside and blow the dust out. Now re-assemble heater and drum. Slip new belt over drum and offer rear cover / drum into place, front edge of drum just sits on two plastic rollers.
The only tricky bit of the job is getting the belt onto the motor spindle AND around the sprung loaded tensioner pulley. Much easier with two people I suspect, but I did it on my own by taping belt to drum to stop it escaping, then tipped machine backwards and did it by feel through the front lower cover. If your tensioner fell apart before you got to see how it should sit, the pulley is attached to an arm that just slips onto, and pivots around, an extended lug on the corner of the motor, above and to the left of the motor's spindle (viewed from rear of machine.) The spring clips onto a small but obvious lug at about 3 o'clock on the motor body (again, viewed from behind.)
Ed Vine, October 2008