you could try searching around for some password cracking software on google, and see which one actually works, they are pretty good from what i hear. my dad's friend used to be like a hacker along with his friends, so they used to work at kinkos, and they use an application back in the 1980's called joshua, which went through every letter, number, and symbol until it found the correct one. and it did this to up to 14 characters. it only worked on pcs though. im pretty sure there might be something like that around these days. anyway if its a dmg, wouldnt it just be easier to redownload the file?