I've seen little message board signature thingies that display the OS and (proxy) IP addresses of whoever's browsing that webpage. I figured that it was some sort of javascript function or other
Is this what your talking about? http://www.neg.be/php/checker.php

As for this dude knowing your OS and other stuff ...maybe you have a trojan on your box.
That would explain how he knows this. Who knows that`s just a thought.

Mike