I have the same problem and Im using a retail 1.6 fallout 3 with all the DLCs. Like If i goto Underworld anytime I get close to the door, BAM crash city. Consistantly everytime. If i try to go into the Druid place up north, BAM crash. If I go into the submarine in point lookout, yes, you guessed it a crash. All of this happens everytime, even if i disable all my mods and just use the Vanilla FO3+DLCs.