In Fallout 3 if you run into a person who has an option of [100% SPEECH] just talk to them over and over again. After about an hour you'll be level 20, congrats to you.

This is because you gain XP each time you successfully persuade someone through speech, and the 100%s, never go away, so you can do it for eternity. I found my guy in "Big Town" after saving everyone, although you can do it just from learning who Bittercup used to sleep around with, and then ask "Flash" (I believe that's his name) about the relationship he had with her. I only had enough paitence to gain a whole level (From 7 >>> 8) but I'm sure you can do it the entire time. So far the PC version of Fallout 3 is great, it's crashed a few times, and I wish I knew how to hot key weapons, it's getting annoying switching through menus all the time. I'd also like to take this moment to thank Ubisoft...