There's not enough information to help much, but you're right, you should be getting much higher fps on Halflife with that card. Try switching Halflife from DirectX to OGL or vice-versa, or try different drivers (with a Geforce3 I prefer the 28.XX's.. they're the fastest for me... find out which are the best for the 4200). Or maybe something's not set right in the drivers that's slowing it down....