If you can hear the congestion that easily I'd get the snake to ta vet pronto or find someone with Baytril who knows how to dose your snake based on weight. Being at UF there are plenty of vets in that area that deal not only with herps but prefer to deal with snakes...I'd find one and get the snake on anti-biotics right away. Remember that snakes are master's of disguise, to include their illnesses, and that if you can hear the congested breathing my guess is that it's further along than the folks at the pet store told you.
Pet stores will tell you anything and now that they've told you what "they" would do if something happens to your snake then they can claim they told you what would have saved it - a cheezy but routine way pet dealers handle customers and a way to avoid any responsibility for selling you a snake that was already sick or exposed to a disease.
Like Keith said, it's not that easy. I'd clean the cage with at least a anti-bacterial soap, rinse it well, put nothing but paper towels and a small water dish for the snake to drink but not large enough for him to get in to and put a heating pad on low heat under at least half the cage; make sure there is good ventilation and maybe even drap something over the front so the snake doesn't feel stressed.
To hell with feeding him right now - if he is otherwise OK don't feed him until he's over this; the last thing he needs while fighting an infection is using energy digesting and then crapping out both feces/urine plus the bacteria in him inside the cage. If he's been eating well up to this point, he can easily go without food for a couple of weeks.
But I'd still find a vet who can tell you what to do in your situation; what I just said is a general assessment based on what I - and just about everyone else on here who's kept snakes for long periods - have experienced.
-John
