Yep, like MrMacMan said, you can run it on older systems. there's a utility fix that lets the installers run on older macs. BUT: two things about the 3400 in specific. First, it only goes up to 10.1, jaguar itself isn't supported as of yet through the fix. Secondly, SLEEP WILL NOT WORK. when you shut the screen, and open it, it WILL crash. You can manually disable sleep, but it's not really a desirable option.
So really, for practical use, there's no way to run X. I'm disappointed too, i love my 3400 but it's just going to have to live with 9.1.
sorry...
pnw