fix one side to the centre of the stud, top and bottom of the cabinet. On this side drill small pilot holes through the plaster and then use heavy duty screws or bolts to screw through the pilot holes and then into the stud as far as you can without it pertruding into the room behind!!
for the other side which will have to go solely into plasterboard use redidrives or back anchors - try and use three or four on this side if possible.
It should be fine - I have a wall mounted LCD that is about 15kg using this method and it hasnt budged (yet!)
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