Fallout new vegas on radeon 5570-Intel Pentium dual core E5400

Just some gameplay on my system i have sometimes lag but that is because it loads sometimes a part of the world. without fraps i just have no problem at all i just run above 40FPS My system: Intel Pentuim Dual Core [email protected] (no overclock) ATI Radeon HD 5570 1GB DDR3 (Overclockt) 4GB Ram DDR3 1333Mhz 500GB Hard Drive 7200RPM