Ive searched everywhere and can't find a solution that works for me. I'm experiencing very choppy game play on New Vegas. Can anyone suggest a way to fix this?

System: Alienware Area-51 desktop
Microsoft Windows XP Home SP2
Phoenix - Award BIOS v6.00PG
Intel® Pentium® D CPU 3.00GHz (2 CPUs)
2GB RAM
DirectX 9.0c
NVIDIA GeForce 9800 GT
Creative SB Audigy 2 ZS Audio


Shouldn't this configuration be able to run Fallout?