Tools required: Phillips size 0 screwdriver
Before starting, note that the HTC Touch Diamond has quite a lot of screws holding it together which vary in length, so it would be a good idea to make a diagram or write down which screws go where. First remove the battery cover, battery, sim, and stylus. Remove any screws which are accessible. You will probably be able to see other screws but not access them at this point.
Remove the charger port/sim slot cover and any more screws you subsequently have access to. Two ribbon cables need disconnecting (circled). One has a piece of white tape covering it which needs to be removed. Then flick the latch up to release the ribbon. The other cable is a thin wire with a small round connector on the end. This attaches like a plug and socket and can be gently lever up with the edge of your fingernail. Now lift the circuit board away from the rest of the phone.