Instructions
Turn on the Wii.
Click the Wii Options menu on the bottom left of the main menu.
Click "Wii Settings." In the top right-hand corner of the screen should be the letters "Ver" followed by a number. The number is your firmware version. Versions newer than 3.2 will not load a DVD-R boot disk; Version 4.2 will not load a boot disk like Homebrew.