CS:S using the CPU more than the video card, compared to most other games. However, your CPU is not causing it entirely, but it is part of the problem. 1GB of ram in vista is not enough to run games, even CS:S. You old video card had what 128mb of ram? Remember, vista uses more system ram when you ahve more video ram to cache/swap things. It's very different than xp in this regard. So, only having 1gb of system ram with a 512mb video card will cause problems when trying to run a game no mater what settings.