When the GameCube was initially released there were two plugs in the back of the unit. One was for the standard AV plug that was used in previous consoles like the SNES and the Nintendo 64. The other was for a Digital AV plug which was used for Component Video and Digital Sound output.
To save space, money, and time the chip that was used to convert the digital signals to analog signals was placed INSIDE the cable (inside the plug that was connected to the GameCube).
Although the cable was meant to output Component Video someone managed to hack the chip to make it output RGB Analog Video instead. The hack is simple in concept but a little tricky in execution.
The cable was only available through Nintendo and was not sold through game or retail stores. Because of low sales of the cable Nintendo decided to remove the Digital AV plug in newer versions of the GameCube although you could still have the plug installed if you wished to have it.
As of February 2006, however, Nintendo no longer manufactures the GameCube Component Video cable.
Once the cable is modified the GameCube outputs great 15Khz RGB Analog video and does an excellent job on 31Khz Progressive Scan RGB Analog video.
However, most of today's VGA monitors won't do 15Khz RGB so you have to make sure that the GameCube game you are wanting to play on a VGA monitor is Progressive Scan capable. A lot of GameCube games, including the Game Boy Player, do support Progressive Scan but it should be noted that only the NTSC releases support it.
