hmm, many of the new hair dryers have the ION stuff- I don't know if that would be OK or not..
but an old one should be ok ..
I would start with a low setting first to see how it goes..

with computer off and unplugged ...

A couple places I read that it's best to keep the fans from spinning when you blow air inside the case.
I didn't know that and mine were going like crazy...

If your computer is real dusty unplug everything and take it outside.. on a dry day .. I should have done this too, I made a big dust cloud in the room...