I recently purchased fallout 3 on steam for the pc, and I am having lots of crashes at the very beginning of the game (birth scene).
I have tried the fix where you change the bUseThreadedAI=0 to: bUseThreadedAI=1, and then add the line iNumHWThreads=2, and i am still having freezing problems.
I know that my computer can handle the game, I have a gateway DX483101e with an upgraded 500w power supply and a xtx radeon hd 6750 video card.
I am also running windows 7.

Please help.

What are the specifications for your CPU? Did you load the game outside to UAC?. Did you max out the graphics before you started the game? Are you running any mods?

I have a quad core intel i3 cpu
Not sure what uac is, I tried to install the game outside of my program files but couldnt find a place to put it.
And I have tried all settings,
and i have no mods.

UAC is User Access Control. It is a security feature that blocks access to most of your computer files unless you are an administrator or have set it up to allow only certain people to have access.
I am not sure how you install from Steam but if you get a choice of a default install or custom install, take the custom install and than direct the install to a location of your choice. For example, you could say to install to
C:\Users|"Name"\My Games and the program will create all the necessary folders and files. I have mine loaded at C:|Bethseda Softworks\Fallout 3\Fallout3.exe. At the launch screen before you start the game, go to setting and turn down all the graphics and than try to run the game. If everything goes well, than you can start to increase the graphics settings.