Hi Glenn.
Yes it is possible to tile directly over Gyprock, depending on the application. If you are tiling a wet area (bathroom or laundry or the like) then i would strongly recomend tile underlay and water proofing priod to tiling.
Don't forget to plan out your tiling b4 you start. Nothing screams "Unprofessional finish" louder than a poor tiling job.
Tiling isn't that difficult, however the trick between a good job and a crap one is in the prepartation.
Even if you spend 2-3 hours just planning the layout, it will be worth it.
Good luck
Gecho