In the L4D2 Demo it does the same but some times it will even freeze on the loading screen and it's far worse in L4D2 than TF2 (BTW it only freezes when I try to go online, Single player plays fine).
I've manged to play some online games with L4D2 but most of the time it will freeze, on the contrary TF2 will play most of the time but it freezes every now and then.
I was using Windows 7 RC and recently switched to Windows 7 Ultimate (64 bit ver). My other PC games play fine they do freeze from time to time but that's normal since it only happen maybe once a month or something but with Valve's games it's very often when I try to play online.
Here my specs:
CPU: AMD Phenom II X3 720 AM3 2.8GHZ 7.5MB
MOBO: Gigabyte GA-MA770-UD3
GPU: XFX Radeon HD 4850 625MHZ 512MB
RAM: Kingston 4GB (2x2GB) DDR2 800MHz
I have both games on pretty much max settings on 1360x768 resolution.
Appreciate any help I can get.









