you using FRAPS? now i havent worked with it in a long time, but back in the day (when i was rocking Dial-up and an Athlon XP) FRAPS used to just kill my frame rates (I used to try and capture my epic battles in PlanetSide or Asheron's Call).
one of the first things i do too, is open the MSCONFIG, and under start up, turn off everything but the bare essentials. some say to go into services as well and turn stuff off, but unless you know for sure what it is, i wouldnt mess with services too much... wrong thing and you get headaches and need to go to a restore point if thats turned on.
give us specs, or make n model atleast and ill see if theres more that i can help ya with.
I have tried Cam Studio, Camtasia Studio, FRAPS, WeGame, and many other stupid capture programs and the one that causes teh LEAST crash is WeGame, so I use that but even without WeGame HL2 lags (FPS lags not internet lags) on LOW settings. Now I KNOW something isn't right... Here is the picture below to the RECCOMENDED specs and my specs.
EDIT: I just did a test out of curiosity and according to the specs, my laptop can run Batman: Arkham Asylum on low. So why is it that it says I can run a next gen game on low but I can run a game from 2006 on low?!?!?! I'm furious, this is why I hate computers lol