I need help on digital joysticks protocols

[zilogz80]

I'm from Argentina (sorry about my poor english)
I built a digital to analog interface to joystick pc port using a pic microcontroller and digital potentiometers.
Here in Argentina digital potentiometer`s ics are very expensives so I have a new idea.
I want to make same interface using just one pic and using digital protocols like comercial joysticks
I found very interesting details here
http://chip.ms.mff.cuni.cz/~pcguts/input_devices/specs.txt
With that info I tried to emulate sidewinder, one gravis and one logitech but no luck for me
I'm sure I'm doing things well acording to the info and I have experience designing with microcontrollers.
I need more detailed info about protocols used by that joysticks (Digital Overdrive from Microsoft, GrIP from Gravis and Logitech protocol)
I don't own any digital joystick to datalogger it
Please help me if anyone knows exactly how that joysticks works.
Thank you all!