Kaktus,
I don't think you need a visa to visit Puerto Rice. It is more like visiting Alaska or Hawaii... you are still within US jurisdiction. So, go and enjoy the sun and beach in puerto beach...
However, I have found out that people who had overstayed their visa are afraid of traveling across Uncle Sam for fear of being caught or detected. So, if this is the case, be cautious. However, domestic traveling is different from international, you only need a drivers license. If you don't have one, then you could raise suspicious of screeners, unless you are bound for international travel. As for domestic travel, most people use their DL.
Enjoy the island, and make sure you eat the food there... very very delicious....