Hi Abianco

I know how, it's not easy but it's not hard.

PS2 controllers use SPI to communicate, so you should be able to easily read data from it using a microcontroller.

You also need the same microcontroller to pretend to be a classic controller. This means it has to become a I2C slave device. There is also some sort of encryption that goes on the I2C bus. I have already written the code to take care of all this. Check my website http://frank.circleofcurrent.com/index.php?page=wii_ext_code

You need to combine these two concepts together. You also need to know the device ID for the classic controller and packet format for the classic controller. Translate the data from the PS2 controller into the packet format for the classic controller. The ID and format information you can find online, I usually go to wiibrew.org

To get started, why don't you try reading data from your PS2 controller and printing it onto a screen first, then translate the packet format and print out the packet on the screen to check if it is correct. These are the two easiest steps in your project.