I think you'll have to elaborate on your issue. A lot.
I downloaded the GECK file for NV then followed the forums intructions on installation as per the GECK forum thread sticky: "how to install the GECK"...moved GECK file to program files/steam/steamapps/common
My System is as follows
ASUS M3A78-CM American Megatrend bios. ver. 1203
AMD X4 940 @ 3.587 GHz
4GB DDR2 @ 900 MHz
ATI 4870 @ 790MHz/950MHz w/ Latest Drivers installed
Win. 7 64 HP
Running FalloutNV Ver. 1.2
If you need more info. like that big old readout of drivers and such then let me know... I am at a loss