Need help on creating Pspice Model

I want to use GALI-24+ to design a RF amplifier circuit and now I choose Pspice for circuit simulation. While I cannot find GALI-24+ model so that I need to create it myself. I have the datasheet and tested S-parameters but I don't know where and how to start. Is there anyone could give me a tutorial or hint how to do it?

And after designing the PCB, I need to extract parastic circuit for post-simulation, what's the most convenient tool should I use?

Thanks!

Tim