The required file is part of the QT3 libraries. The Gambas IDE depends on the QT components to display the IDE. Also many Gambas components are based upon the QT ones.
You should make sure the QT packages are installed along with the associated devel packages. It is best to use your package manager to do this so there are not conflicts with your current set-up.
On SUSE the required packages are called qt3 and qt3-devel. They should have similar names on Zenwalk.