I have written a couple apps in perl Tk, and it's not too bad once you get the hang of it. The O'Reilly book is OK, but not great, some examples to get you started, but I'm still not sure whether it was worth paying for. I think I learnt more about Tk by grabbing a bunch of perl Tk applications and browsing through the source. The nice thing about this is that you don't really have to understand what the program is doing, as the GUI creation is seperate from the back end.

Having said that, Tk is nice for cross platform applications, but for something that would look more like an actual windows application you might want to look into Win32::Gui instead. I have little experience with this, but it does create a more window'sd look and feel than Tk does.