I saw a write-up on how to build an O2 emulator somewhere when I did a google search. You just need to buy about $6 worth of stuff from radioshack and get to soldering.
if youre talking about a resistor setup, that doesnt work. the signal from the sensor is a WAVE, not LINEAR.
they used more than just resistors... I can't remember exactly what it consisted of. There is a writeup out there somewhere, Im just to lazy to find it again lol. But they said it worked.