You will see something to this effect in the details of the error:
Fault Module Name: xlive.dll
Exception Code: c0000138

I fixed it up updating the xlive.dll from Microsoft.
Go to:
http://www.microsoft.com/downloads/details.aspx?familyid=05013300-5d14-4dc9-9145-991ea1b8e4b0&displaylang=en

You will then download “xliveredist.msi”
Make sure to close all your games and then double click on it to install the application. After a reboot you should be good to go.

Newly released is the G.E.C.K. (or Garden of Eden Creation Kit). The G.E.C.K. allows the community at large to create, modify, and edit any data for use with Fallout 3.
Download at: http://fallout.bethsoft.com/eng/downloads/geck.html

Visit the G.E.C.K. Wiki for help and tutorials:
http://geck.bethsoft.com

For those who have never played Fallout, it is basic premise that World War 3 happens. The depth and richness of the post apocalyptic world of Fallout 3 is immersive and completely addictive. All throughout the world there are bits and pieces of pre-war world which was a throw back to modernized 1950’s America. The whole pre-war world is very tongue and cheek and the violence in the game is just as over the top. Through the use of giant bomb shelters call vaults, sold by the Vault-Tec company, your character’s ancestors survive. And as the game starts, a hundred or so years later, you have to help save the people of the wasteland.

Beyond the main plot there are many story lines and lots of side adventures. You can ultimately explore the whole world as you advance in skill (level). While adventuring you talk to various people and your deeds give (or take away) Karma, depending on your Karma rating, good or bad, the world treats you very differently. Fallout 3 still keeps the interactive aspects and character building of previous versions with the addition of a first person option for more real time action. The old turn based combat is still available functions well.

Fallout is a throwback to a game I used to play called Wasteland. If you want to see some old screen shots check this out:
http://classicgaming.gamespy.com/View.php?view=GameMuseum.Detail&id=209