Playstation 2 connection with USB or FireWire?

eptica, it sounds like you are asking if you can use the iMac G5 as a screen to play your PS2 games system through. I am afraid to say that the screen will only operate with the computer - i.e. you cannot have any external visual input into the iMac G5.

In short, no.

P.S. You can physically connect them, but nothing happens.

You would need some sort of video converter to do this, like Elgato EyeTV or one of the Formac converters. You would get noticable lag from the conversion, however, so it would not be a very good gaming experience.

] Can I connect a PS2 on my iMac G5 with USB -> USB or USB -> FireWire 400?!

The eyeTV Wonder USB 2 does allow you to connect your PS2 to your iMac and use the screen.

http://www.elgato.com/index.php?file=productseyetvwonderfaq#faq14

Q: Can I connect my PlayStation/GameCube/XBox to EyeTV Wonder USB 2.0?

A: You can. EyeTV Wonder USB 2.0r has a delay of only few milliseconds, allowing for excellent live gameplay. Other EyeTV devices have encoding hardware that causes a larger delay, rendering gameplay difficult to impossible.