My parents have a really dusty PC and I was just going to use compressed air to get it all out, is that the best way to do it without damaging parts?
yeah basically. And clean the rest with rubbing alcohol on a lint free rag if you have to.
My dad uses a vacuum, with this air sucker thing attachment thing. It works well.
Use a vacuum, but make sure all the power is disconnected because a vac might create some static (but most likely won't) air just blows it around, vacs suck it up.
My old work just had an air compressor or something...unlimited air ;)
If you use compressed air, I would do so sparingly if it's coming from a compressor w/out an air dryer on it. You would be surprised how much water is really in compressed air.
just make sure you drain your compressor before each use and you should be fine