I would like to know how I go about getting a copy of my husband's grandfather's birth certificate - it was born in Tripoli Greece. Is their a form or service I need to use or can I go through the embassy?

It's very easy: go to your local Greek Consulate with your husband's grandfather's name and approximate year of birth. They will then contact the Municipality of Tripoli and see if he is truly registered with the Military Records [like all men his age were... this is called the "Mitroa Arrenon" in Greek]. Assuming he was, you'll be all set.