That said, most all Fallout New Vegas mods work in Fallout 3. There are a wide variety of ported mods available on Nexus (search by TTW), but it's not nearly all of them, especially as I like the really involved quest mods (Arefu Expanded, Quest for Heaven music version) and a bunch of environmental changers (Bond's Tenpenny Tower, Vaults Rebuilt, Bigtown Expanded), and there's no guarantee at all the modders will take pity on you, especially if it's a complicated mod. I need personal instruction to understand anything and video tutorials don't count. That said, if you heavily mod, or like my consider heavy modding a simple REQUIREMENT to make Fallout 3 playable (I consider Bethesda games to be horrible in general MODDERS WILL FIX IT!), you're going to run into problems as Fallout 3 mods can be converted, but the process for all but the most simple is difficult and the mod community expects you to teach yourself, something I am incapable of doing. There's a bobblehead mod that gives unique bonuses to bobbleheads in lieu of stat bonuses. New Vegas has less horrible bugs in it than Fallout 3, greater options and stability and I found the fights were better with riders, much more in terms of gun variety and it seemed more plausible for the weapons loadout. It didn't work with my disc copy, but that was 1.3 and they're on 1.7 now

You DO need copies of both games, preferably the Steam GOTY and NVUE. Tale of Two Wastelands, which is not directly supported by Nexus, is a conversion for Fallout 3 and New Vegas to run on the same engine.

T tale of 2 wastelands