I need some help with some gauges that i had just recieved for christmas. I got the autometer EGT, Boost, and Air/Fuel. I had a question about the A/F because i know i need some sort of O2 sensor kit. Autometer makes one but i also heard that i can just buy any O2 sensor and send it into the downpipe and it will work. Can anybody help me out?? Any insight is appreciated! Thanks!

If that's the cheapo Autometer A/F gauge it is of no real use in measuring anything so if you want a truly useful gauge don't bother installing that one. It's usually tapped into the rear 02 sensor which is too far downstream in the exhaust, not to mention being after the cats and a narrowband sensor. You can add a separate sensor but with that gauge it would have to be a narrowband so the readings still won't mean much.
Sorry to say but if you want more than just blinking lights from an A/F gauge you'll have to cough up some $ for a real wideband one. OTOH unless you have sufficient mods done to your car an A/F gauge is not a necessity.