The name SAP is acronym for Systems, Applications and Products in Data Processing. SAP is an extremely complicated system where no one individual can understand all of it.
SAP runs on a fourth generation programming language language called Advance Business Application Programming (ABAP). It have many of the features of other modern programming languages such as the familiar C, Visual Basic, and Power Builder. Your programs name conventions begins with a letter yxxx or zxxx.
SAP graphical user interfaces (SAPGUI) runs on Windows / NT / Unix / AS400. When you are using 3.x you can used the SAPGUI 4.x, ECC, there are no conflicts as the SAPGUI is basically a front end tools.
If you create dialog screen, remembers to tick Development Tools (utility programs for the Screen Painter) when you are installing SAPGUI 4.x.