Fallout 3 Paradise Falls?!?!?!?

You can change which quest to focus on in your PipBoy under Data>Quests. It sounds like you have access to Little Lamplight in which case you should be able to talk to Mayor McCready, if you can find him, and ask him about a secret way into Vault 87, if you want to continue that quest, which by the way is almost the end of the main quest and the game. I suggest you wait and do a lot more exploring, especially if you haven't found Paradise Falls yet, which you have to find just by wandering around the wasteland.