Well, I'd recommend Glade
if it's really what you need. It would help if you indicated what programming language you're using.
And, (my biased opinion ahead), don't automatically assume that just because a development environment is GUI, that makes it the easiest option. I've worked with some dozen languages, and I always consider GUI IDEs as a pain in the *. Since, in order to make that window with the buttons do what you want it to, you'll have to go into the generated source code and edit it anyway, you'll have to know your way around the programming language plus you have to learn this new IDE tool and get used to the code that it generates - which will be based on what *somebody* *else's* programming class professor thought was the *right* *way*. Oppose this to a plain old text file where you write the code from scratch in an editor you like, and a good book on the language to help you along. That way, your only challenge is the language itself. Since all you want to do is a simple application, both Tcl/Tk and Python-with wxWindows or PyGTK will be very easy to make a simple interface in. Have you even considered whether you need to bother with a GUI at all? If it's really simple, maybe it can just be a command line program?
My purpose with the above is *not* to steer you in any direction. It's your program, you know what you want, not me. I just wanted to toss a couple considerations out there. Many people new to programming may have all kinds of misconceptions which can actually make it harder for them to learn.