I can start App store and browse through apps but as soon as I press "install" it kicks me back to the home screen. I can get apps if I am synced to my Mac so it's not a total loss but is there anyway to reinstall the App Store to my Iphone 3GS?
Try powering on or off, then reset all settings if that does not work. If still nothing you may need to do a restore, there is no way to reinstall app store by itself.