Are you referring to the categorized tabs, such as Applications, Settings, Games, etc.?
If so, you can change the configuration, or eliminate a tab completely, using the TabManager application. If you are Linux savvy, you can also do this directly: each tab represents a subdirectory of /opt/Qtopia/apps. Every icon displayed on a particular tab has a corresponding .desktop file in the subdir for that tab. You will not see changes you make to the configuration until you refresh or restart Qtopia.
BTW, the last tab (FileManager) is hardcoded into Qtopia, so it cannot be removed by a simple configuration change,