The Samsung Galaxy Tab has a large 7 inch screen. This causes some problems for some of the apps in that they don't scale out to use the full screen by default.
Good news is that a handy app is available in the Market Place that allows you to change settings and stretch out those games and apps that run at a smaller resolution.
The technique requires that you install an app, disable and enable an option in the new app, reboot, disable the option again and then reboot. If you follow the instructions (in a lot more detail in the video below), you'll be able to run all apps full screen.