Where is the starter on a 2002 saturn sl a diagram would be a help and how to change it

crawl in between the engine and the firewall from underneath, it is by the starter.

Could be starter, battery, battery cables, security key system module going bad, etc.
Check easiest things first. Battery condition and age, condition of cables, and connections at starter.

should be at the end of your top rad hose

Can you clarify a little better . does not crank ??? As when you turn the key to the start position nothing happens ? The starter does not engage an spin the engine ? Control module has nothing to do with that . Park neutral safety switch maybe, ignition switch possibly, main B+ cable from battery to the starter solenoid. If you would look at a wiring diagram to see what all is involved in the starting system on your vehicle an testing the starter electrical circuit's . Doing voltage drop testing on the starter main B+ circuit .. Starter Voltage Drop Don't keep changing out the starter , that is not it. Free wiring diagrams here http://www.bbbind.com/free_tsb.html Enter vehicle info. Year , make , model and engine size. Under system click engine ,then under subsystem click on starting . Click the search button then the blue link. Now look at the wiring diagram ,DO YOU SEE A CONTROL MODULE any where on that diagram ??????
You should learn how to diagnose be trying to fix cars.
Electric Testing Techniques You Need to Know

some ecm boxs have to be rest by a dealership to work with car specs, usually not to high 100- 200 dollars

Hope this diagram helps: http://www.autozone.com/autozone/parts/1993-Saturn-SL/Starter/_/N-j012uZ93xl9
Make sure you disconnect + battery cable before removing starter.

your battery is dead

Watch this video and have at it.
http://youtu.be/1E9oWefCI0s

Sounds like a thermostat problem to start with. Follow the top rad. hose to the engine. You will have to bleed the system of air after.

Voltage drop testing the starter electrical circuit would be a good first step , ruling out the cable's connections an ground !
Starter Voltage Drop If this doesn't find a problem ,then check the control side . Ignition switch , when it won't start check for Battery voltage at the connection at the starter solenoid "S" terminal .
How to voltage drop test starter motor circuit