start with the simple things, battery terminals like Mt said.
baking soda in water removes corrosion really well, then remove oxidation with sandpaper. track all the black wires from the battery to their connection points, make sure these are clean and making good contact.
here's a link to wiring diagrams
http://www.autozone.com/servlet/UiBr...3d80119101.jsp
cut n paste it into the address box in internet explorer. hit the enter key.
the battery can be ok, the alternator can be ok, but if the voltage regulator on the alternator goes out, the battery doesn't charge correctly and the batter doesn't have enough amps to start the engine.
to test the battery, alternator, and voltage regulator you'll need a digital mulimeter, which you can get for about 20 bucks (u.s.).
check the batter connections and ground connections first and post back.
I'll dig up the testing procedure for the alternator/v.r./battery in the meantime.