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
if you can check to verify, but from what im seeing, it looks like your graphics card is integrated and not a stand alone mobile gfx card. the problem with that is, is that the memory is shared between the graphics and the rest of the system. HL2 is also very Physics heavy... so its hitting the graphics card and its memory, plus the CPU and its memory... im a bit drunk watching the Bear game, and i dont have HL2 installed to check myself, but see if you can disable the Physics (maybe labled PhysX) in the game, and that may help alot.
also gotta remember that while yes HL2 is an older game.... it was completly revolutionary when it came out, and brought new systems to thier knees when it came out. and Valve never leaves good enough alone, they update the code quite a bit.
so im thinking that the integrated graphics with shared memory, along with the physics of the game may be your problem. course ive been drinking most of the day, so someone may come in and shred this theory.... but its what im thinking.