It's not his hardware though, it's been stated numerous times that a number of people playing this game recieve memory read errors.it could be ture but its quite not, sorry. it is all in his hardware man, he has somethig worng somewhere and i think its drivers myself.
Try tightening your memory timings again after using this fix and see if it solves the problem as I don't think you should have compensate by keeping them loose.Here is the fix:
First location:
Right click your Half Life 2 icon on your desktop (the one you would normally double-click to launch the game). Then click Properties. Click the Shortcut Tab. In the line labeled Target, you will see something like this, depending on where you put the program when you installed it:
"C:\Program Files\Steam\Steam.exe" -applaunch 22
Copy and paste the following AFTER the above line:
+mat_forcehardwaresync 0 +snd_async_prefetch_priority 1
Be sure there is a space between -applaunch 22 and +mat
Click save and you are ready to go.
Second location:
From the Steam Play Games Menu, right click on Half Life 2. Choose Properties, then click Launch Options. Paste the following in the box.
+mat_forcehardwaresync 0 +snd_async_prefetch_priority 1
Click Ok and you are ready to go.
Do the same fix for Half Life 2 Deathmatch and Counter Strike Source.
If that still doesn't work it seems that your memory is starting to fail on you, but I'm confident it is simply a HL2 problem as you've said it doesn't happen anywhere else.