No problem! First of all, welcome to our forums.
This page has all you need to know about the file to edit. If you're modding the PSX version you will need to look at the WINDOW.BIN file as you say.
Then you'll need to know about the
compression method it uses.
You'd also need to know about the
graphics format or you can use someone's tool to translate the image between more conventional formats. I don't know which one to use, but plenty of other people do.
After that, just modify the way the image looks and keep track of which characters are going where when you do the translating.
That's not a very detailed explanation, but hopefully you can figure the rest out.
