Fri 27-Jan-12 03:58 AM | edited Fri 27-Jan-12 04:00 AM by avm247
Well, I would be careful and I would use a bulb blower (like the Giotto Rocket) and blow some air in the mirror box while holding the camera with the lens mount facing down, any dust you move around should fall down and out of the mirror box.
It is typically NOT recommended to use a canned of compressed air as it may blow the propellant into the mirror box and cause you more problems than it solves.
Mirrors are front coated, rubbing too hard might rub off the silver coating. Using a lint free cloth (like a microfiber cloth) you can try and wipe down the mirror and the focusing screen. Be careful not to rub off any foam seals (that cushion the mirror when it flips up) at the top of the mirror box.
If you don't wish to tackle this, any repair place should be able to clean the camera for you. If you send it to Nikon, an authorized repair facility or any repair place, you should be able to get them to perform a CLA - Clean Lube Adjust - on the camera, especially since its been sitting for a while.