You may want to pick up a book on Photoshop to help you along. While it won't be specific to the gimp, that program borrows heavily from what's in Photoshop, so there are always equivalents. Likewise you can get by with a book on PaintShop Pro or Corel PhotoPaint if they exist. I mentioned Photoshop because it's the professional's choice and the subject of most published books.
Another good idea is to do some searching on the web for tutorial sites that discuss Photoshop/Gimp/etc basic use. Most of them will have tutorials on making all kinds of button-like graphics.
Such an illustrated approach is going to be a lot more helpful to you than any amount of email while you're starting out. Being on the advice/tips giving side is also very difficult through email. Once you have learned a bit about the graphics basics, I'm sure some tips in email about how to use those graphics within ProntoEdit would be far easier to follow.
Just some advice from someone that's been using email and graphics applications for nearly 20 years - I couldn't imagine introducing someone to graphics editing (in general) via email.
