Anyone knows about a guide or something to use a Playstation 2 controller on a USB port.

sometime ago i've read a guide on how to convert ps2 pads to pc, you need to buy an extension cable for ps2 pads, then after some changes you'll be able to connect it to the serial port but for force feedback to work you need extra power so blah blah blah...
the easiest method it's to buy a ps2 pads converter for about $15/$20, i personally own 1 named "EMSUSB 2" that let me play with my 2 ps2 pads on my pc using the usb port. you can google but i don't recommend it because my force feedback function don't work very well dunno why
also google for SmartJoy, PS-PC USB Converter III, PSX/N64 PC USB Adapter...

I have seen a lot of those Converters, but i do not whant to buy it

I have seen how its possible to use Xbox controllers and i was hoping i was possible to do something like it with PS2 controllers.

Using a serial port on PS2 controllers is not an option really, i do not even think i got a serial port on my computer.

I paid $25AUS for a PS2PC converter called, funnily enough, PS2PC created by an Australian company called TruBlu.

You can get the converters for cheap enough and it's a lot easy then making your own.

USB is definately the way to go. Anything else and it's really to slow to be any great use.