It's not a difficult job, but is a fiddly one.
Gears sound like the problem with yours (particularly if one side moves differently to the other), and cost a couple of quid each. Changing them is not difficult; a #2 pozidrive screwdriver is pretty much the only tool you need, but the best advice is to ensure that you FULLY understand the system beforehand. Go and have a LONG read of the clarks garage page on "Sunroof" (here: http://www.clarks-garage.com/ ), and follow the links under "Garage Shop Manual" - read the overview as well as the section on replacing bits) and only start to tackle the hardware once you are sure you know what is going on.
Grease everything throughly and take your time. A good tip for a place to start is to slacken off the sunroof clutch to the point where it doesn't work, and tighten it very gently until it just starts turning. That way you won't damage anything if you get it wrong.
Oli.