Matthew Debacco has created an excellent guide with pictures to help identify pumpkin plant problems. I have posted his guide here: Pumpkin diseases and plant problems
Information about pumpkin diseases can be found here:
Pumpkin Disease Information
Additional Pumpkin Disease Information
Insects that do damage:
The cucumber beetle is my number one enemy each year. You can find information about this insect and how to control it here:
http://vegetablemdonline.ppath.cornell.edu/factsheets/Cucurbit_Beetles.htm
http://www.attra.org/attra-pub/cucumberbeetle.html
http://www.bhg.com/gardening/pests/insects-diseases-weeds/stop-cucumber-beetles/
Information about the vine borer can be found here: