Do i need a visa to be in mexico for one complete week?

You will get an FMT, tourist card, at the border or on the plane. It is good for up to 180 days...just tell them you are staying for a long vacation and need the full 180 days. You do not need any other kind of visa, unless you plan to stay in Mexico and reside there or work there. See site below to verify this information. this applies if you are an American citizen or permanent resident, or a citizen of one of the other countries listed on that page.