Graduating in May -- Let the job search begin

Hello all!
I will be graduating in May with my ADN. I have already started searching for a RN position and I have a few questions. I have applied at a couple of local hospitals (in Virgina) but I haven't heard back from them. How often should I contact prospective employers if I haven't heard from them?
Also, I am having clinicals at one of the hospitals that I have applied to. Would it be unprofessional to stop by the Nursing administation office after clinicals (usually around 3pm) or should I make a special trip (about an hour away) to talk to them.

Thanks for your help
The Emmy