linux development
There are three good options for gui development in X:
Kylix - very easy if you have delphi background, as it shares the same interface library, but if youve never done delphi before then its probably not the best choice.
kdevelop - pretty easy to use, the ide still has bugs here and there, but nothing you cant work around. It makes developing Qt apps reasonably easy. Qt is a very nice freely available library for writing x apps, well worth learning, and it comes with a great online reference.
Qt Designer - comes free with qt, and can generate most of the code for your project. If you work through the tutorials with qt then you can figure it out pretty easily. Using this requires some command-line work, but nothing more than a few commands, which the tutorials explain to you.
The main benifit of using Qt is that it is portable, and there is a non-comercial version of the Qt library for windows. It really does simplify doing things like image handling, sockets, etc.