Shared items take awhile to show up?

My airport is always on the shared items list but the 2 other computers and wireless printer take an random amount of time to show up. Is there a setting I'm missing or just ill informed on the subject. The thing is the other computers are always on, one is windows 7 and the other is vista. I can print to the printer, but can't access lets say the memory card on it, until it shows up. They do appear but usually takes some time whether the Mac Book Pro is asleep or restarted. Its kinda annoying if I want to access some files on the other computers and have to wait for them to become available. Anyone know whats going on and can help me? Thanks