In regard to GUI programming, I must say that Perl/Tk is very easy to get into. I haven't really done anything with GTK+ or Win32::GUI, but Perl/Tk was very easy to "get". If you choose to go this route, the resource I used most often (aside from Mastering Perl/Tk) was this collection of man pages.

As well, you probably aren't looking for an outright "hand out" for your notepad project, but if you get stuck (assuming you go with Perl/Tk) feel free to check out medit, a notepad-like editor that I wrote.