I'd like to apologise for the delay once more. I started working on some example code and realised that I was making a tool that might be useful for some other stuff that I'm doing (tutorials et al). I've been working on-and-off so that the app is more solid, and it's slowly getting there (pic). The idea is that you'll be able to choose a tileset and then add your own rectangles, resizing them appropriately. You can then save all the coords to a file for easy loading.

It's still a day or two from completion. I'll try not being so lazy and will hopefully finish it real soon, after which I can get on with showing you some decent examples!