Ok time for some maximum tweaking hehe, we will get it to play good no doubt. First off, how much ram do you have?
First off add these commands, to do it right click on each Source game, L4d2 css, half life, etc and click Set Launch Options. Then add these commands into it
-threads 4
-heapsize 1024000
+exec mytweaks.cfg
( You can see if the above 2 commands help any)
Now, ill make you a Config file to put in your Config directory, ill need your email address to send the config file to you./ unless macrumors can send files to each other.
mohmandm@msu.edu