See the wiki section on cheat codes. there is a boot prompt where you enter the code. It's there every time you boot the disc. I'm not clear on what the dummy group is or why you seem to have the wrong disk, but I'm also confused on how we could have gotten this far in the discussion and you could ask about when to enter the lang=us code, seems like you have not tried it yet, and so I don't know if that's really the issue or if you have some strange hardware (like an other language keyboard) that is causing the conflict.