If you need some extra frames in Half-Life 2 or Counter Strike Source and don't care too much about visual quality, add this to the properties of your Counter-Strike Source by right clicking the game in Steam and properties and set launch options:
You can also add a -heapsize option too, its similar to com_hunkmegs in Quake 3. If you have 512mb of ram, set -heapsize 384000 or 768000 for 1 GB systems.
-nojoy -noipx -dxlevel 70
Basically just set it around 3/4 of your ram. Probably won't make a huge difference either way but it should smooth out the gameplay a little if you're having any stuttering. Also, -nojoy and -noipx, those were used in 1.6, however they do work in Source as well. They should free up a very small amount of ram, but so it can't hurt anyway.
And -dxlevel 70 that is the big one here, especially if you have a older video card or are desperate for framerate. It won't look awful, just remember after you put the -dxlevel 70 in your launch options, after you launch the game once with that parameter make sure you quit and remove -dxlevel 70 from the launch options. Reason why is because it'll keep resetting your graphic settings in Counter Strike Source if you don't. Since I'm sure you'll want to customize them anyway. Another thing -dxlevel 70 does is removes all the pixel shaders.
Hope I helped.