What exactly does "(I/O error - Bad Media?)" mean when trying to take something out of/reading a disc? And it has the same error when copying the thing from the disc in my Backup HD and Macintosh HD... so... what does "I/O error - Bad Media?" mean and how is it caused exactly... and if possible to answer: how do I trouble shoot that bish?

When does that error happen? When you try to copy the Vendetta application out of the DMG file you downloaded? If so, then the downloaded file is probably corrupt. Trash the dmg, download it again and see if it works properly.

Nah, it's for a different game. I take the disc and when I try to install it I get the error. Even if I try to install it to my backup HD or Macintosh HD. I've never had this error with this disc before and it's been in my computer for as long as I could remember... So either my comps effed up or my disc's effed up and I want to know which one, and what Bad Media means and how did it get there. Thank you for helping, btw, I think I might need to torrent the game, though, if it's the disc... if it's the comp I guess I can't take the many errors with our 5 year old iMac and I might as well wait for this one:
http://www.macrumors.com/2007/06/06/no-imac-updates-at-wwdc/
if it comes out and get that...

Oh, trying to read a cd/dvd.

The error means that the system had problems reading data off the disc. Either it's the CD/DVD drive, or the disc. If you don't have problems reading other discs in that drive, then it's the particular one you were trying to use.

Give the disc a clean.