Are there any walk through guides with pictures on how to replace a thermostat for a 98 Monte Carlo?

Yes indeed, there sure are. 1) GM shop manuals for the specific make and model. Your dealer will sometimes let you photo copy or you can outright purchase a copy. 2) Chilton repair manuals. They are usually available at most part stores. 3) Haynes Repair manuals. Also usually available at auto part stores. These manuals are excellent for "shade tree mechanics" (people who aren't full time mechanics but have lots of patience and their own tools).