Apps on 3G S aren't installing

[SlamuwellJaxson]

what's up guys, i'm a noob on this site so bear with me. I just got a new macbook pro and iphone 3g s yesterday and after exchanging the macbook due to a dead pixel, now i have a problem with my iphone. whenever i try installing apps via itunes on my computer, the apps don't show up on the homescreen. whenever i try installing via itunes on the iphone it either gets stuck on installing/waiting or it won't allow me to download an app that i bought because it says 'installed' in the app store and the button is greyed out. do you guys have any suggestions? thanks in advance