Another note, once you get the base graphics working start the game, go to downloadable content and download the zBase graphic pack, which is around 207MB. Those are vastly superior to the OpenGFX pack, and gives OpenTTD a very polished and modern look.
http://www.openttd.org/en/download-stable
I'm fairly certain they're pretty much complete replacements now, but I haven't been able to get the music pack working on Arch yet.