Can anyone tell me where exactly the front o2 sensor is located and how difficult it is to replace on a 2000 LS 3.8 eng.

Any help would be greatly appreciated.
Thank You, Joe.........

Should be just down the exhaust pipe from the rear manifold, may be able to see it from under the hood.

That's right, it's not hard, and Autozone will loan you a special socket that makes it easier. The sensor itself was about $75 when I did mine two years ago.