Joining enables you to download bigger mods so if you like mods, Yes.
Yes, you can install Fallout 3 PC mods from Fallout Nexus onto the PS3. For a tutorial, see: http://fallout-mods.blogspot.com/2010/11/fallout-3-mods-for-pc-on-ps3.html
No,
You can't
In Fallout 3, there was a site called "Fallout 3 Nexus", from what I understand it was where everyone went for mods. Similarly, one was made for New Vegas named "Fallout New Vegas Nexus". You'll be able to find all the mods you could ever hope for there (just google it). Be sure to download the Mod Manager, it makes mods easier to use.
Yes.
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Until the Broken Steel DLC comes out I don't think that you can join an organization.
The unofficial patch often causes Fallout 3 to stop responding or crash to the desktop on Windows Vista and 7. It was fine on XP. You can uninstall the unofficial patch and install the newest official patch on any Windows version and it should run fine. Note that the PC version of Fallout 3 is quite buggy and contains many glitches that cause it to crash. Some have been fixed with the official patch and some were fixed by the modding community. Get a hold of Fallout Mod Manager (FOMM) and get a few game fix mods from The Nexus Forums (Fallout Nexus Mod Archive).
NO! You can get a Fallout 3 disc for PC, but you have to pay for it. And you can't download it. That would probably take up too much gigabites, anyways.
I modded my fallout game and personally i think it completely payed off due to it adding around 3 total new maps of gameplay.
Occasionally Fallout: New Vegas will freeze, but not as frequently as Fallout 3.
fallout 3 psp??????