working on the disco

as some of you know i just bought my first discovery. its a 95. i'm not much of a mechanic but i'm learning. i just did my first ever oil change on my bmw just last week. so.... i checked the rattle under the disco. it seems that the cat on the driver's side is bad. how do i swap it out? are there online write-ups? is there a parts list for our cars thats accessible to us? i ask this because there are site like these in the bmw world and i'm hoping its the same for the land rover community. when i was under the disco i also noticed that there was alot of "wetness" like fluids on the parts. is this normal or maybe a leak somewhere? the engine oil is full and it was not black. the trans oil was red. anything else you guys can think of to check out? the radio is locked. i have the books on the disco and there is a card that has a radio code but it does not work. what can i do about this? thanks for the help!!

Fernando