This is a simple way to make custom backgrounds to put into a .pac file. The header is provided for you, and only supports one texture inside of it so far. You can also choose a .ogg file for music.

The resolution of your background should be twice as wide as it is tall. If it is not, the game will squish the background in the height. If either the width or the height is not a number that's a power of 2, it will be resized to whatever is closest. Keep this is mind if you don't want your aspect ratio screwed up.

.pac files seem to have no real compression, they're just an archive. There's the header, and then there's the files, nothing else is really there in this format. This program is more of a proof-of-concept sort of thing. 