If you bought it as a "refurb" - take it back and complain - if it's dusty, then they never refurbished it. Especially if it has a Thomson drive, lol - maybe they'd just hand you a different one and it might not be a T-drive.
I woudn't use compressed air, for the reason you stated. DamageInc is right - vacuuming is best if you're not planning on opening it. They make them for computers, or just try duct-taping some plastic tubing (like aquarium air tubing, only a little bigger, at any hardware store) to your vacuum cleaner. just be careful - if you use too small of a tube or too strong of a vacuum, who knows what you might suck out of the thing... :lol:
Also, before your return date, or warranty comes up - play a lot of GTA Vice City and watch a lot of DVD's (Chocolat with Johnny Depp is one), especially if it's a T-drive. Those two discs failed several times on my first XBox.