Best advice is to follow the routine described in Haynes manual. I've changed the belt on four different cars with same type of engine 7 times.
Basically you put the car on jacks then independently jack the engine, undo the engine mount offside of the car then take off the cambelt covers.
Before taking belt off, you have to set the pump, crankshaft and cam with bolts to ensure they stay in the same place while you swap the old belt for new. Then you release the tensioners and swap belts - very fiddly job as you have about 1.5" to put your hands and hopefully a friend's too.
Then put it all back together not forgetting to take out the bolts from the camshaft, pump and crank.
This is a basic description but fairly accurate - better with pictures so see a Haynes manual for Peugeot XD engines.
Darren from Southampton, September 2006
