You can test the starter by disconnecting the small diameter harness wire from the starter, and briefly touching a jumper wire from the positive battery cable to the terminal where the harness wire had been connected. Make sure the transmission is in neutral or park, and the emergency brake is firmly set before doing this; as the starter may run. Keep hands, tools and clothing away from the fan belts or moving parts.
If the starter runs when the jumper is connected; the starter is good. In that case; I would replace the starter solenoid relay, shown here (http://www.rockauto.com/catalog/moreinf
o...) If this does not solve the problem; the neutral safety switch (only used on automatic transmission vehicles), or the clutch pedal position switch is probably defective.
if the starter does not run in this test; I would only buy a replacement at a NAPA Auto Parts store; in order to avoid all the hassle that come with buying defective rebuilt parts that commonly are sold by discount parts stores.