Awww poor guy! Croup sucks. :-(
The good news is that the steroids help A LOT and pretty darn fast. There is also something they can give orally in the office (I forget what its called, but it might actually be a steroid come to think of it) that works in a few hours.
Usually croup is a summer/fall illness for some reason, but now that its winter you get the benefit of the cold air outside. If he's coughing a lot, bundle him up in a blanket and go outside for a few minutes. The cold air opens up the airways and helps the cough die down -- its seriously like magic.
I hope he feels better soon! With the steroids, the cough should subside within a few hours.