mackenga

A what!? Joking aside, I suggest wxWidgets for a cross-platform GUI development library. I'm no expert; just started scratching the very surface of it recently myself; but it's looking good to me, and will save the time you could waste on Win32.

For rapid GUI development, check out Tcl/Tk - I know I bang on about it all the time, but that's because it's excellent. http://www.tcl.tk/ - it's a high level scripting language you can extend with C, and you can embed its interpreter in C applications. Definitely worth a look if you've started with C, anyway; I reckon Tcl/Tk is seriously underrated, and as far as language teams go, you'd have to go a long way to beat C and Tcl for rapid development of efficient (enough) GUI apps on Windows, Mac and Unix.