In the older version of CS you were able to manually support yhe video card with more ram from the system. This command takes the ram you allocate and takes some load off the video card. You need to put tis command in the start options of the. To get click play games, right click on cs source, go porperties and load options (I believe). It is in the middle of the window. Clcik the box and a window will popup. This is for input of things the old cs used to use like -cstrike and such. The cammand you will input will be a "-heapsize XXXXXX" Where the 6 x'x correspond to the amount of physical ram your allocating. I have 1gb ram so I can allocate 768mb (768000) easily. I would not allocate more than 3/4 of your ram, or the game will get choppy. If you load to much just go back and change it to a lower number. First set it to half your system ram for a test. If you have 512mb ram set it to -heapsize 256000 and so on.
There are other commands you can us in the console to turn the amount of total fps possible to a higher number. CS stops fps at 72 (I think). To change the amount of total FPS displayed type (i dont remember which one) FPS_max 125 max_fps 125. Also you should check your monior refresh rate, and turn it up to the fastest refresh rate supported ~85hz-100hz.
Other commands you can use next to heapsize command:
-Nojoy (disables joystick, game loads faster)
-noIPX (disables IPX protocol, game loads faster)
-exec file.cfg (exec file at loading of game)
-console (enables console in older cs, but source has a button to enable it)
To load many commands just list them, for example.. here is mine
-heapsize 768000 -nojoy -noipx -console -exec fastbuy.cfg
Hope it helps, send me a message if you need any more help.