need help!!!  arduino SPI programming the MCP6S21

Hi,
Can somebody please help me understand how to program using the SPI library on MCP6S21. I'm using the Arduino Duemilanove(Atmega328) with the software ver 0019.
The MCP6S21 is 8-PDIP from microchip programmable gain amplifier (PGA) using SPI: SCK, SI, CS (only 3 pins - input only).
I've tried over and over again to simply write a program that changes the amplifier gain to X2 but with no success at all. The MCP6S21 basically programmed through the SPI interface using 16-bit words.
From what I see in the datasheet it supposed to be very simple but I've tried many variations of programs like the arduino examples: DigitalPotControl, BarometricPressureSensor or even something more close: /playground/Code/MCP3208
so far nothing worked.

I'm new to SPI and if someone can shade a light for me I'll be very grateful...

if someone can shade a light for me I'll be very grateful...

You are more likely to find help if you don't cross post. That really pissed people off on this forum.