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Run? Probably. Run well? Unlikely.

The integrated video will require a substantial stepping down of the graphics setting, and 1GB RAM will not help your cause. Best thing you can do is upgrade to 2GB.
 
So after about 3 hours I got to play the HL2 demo most of the settings are on high but nothing really happened so I don't know if it would still work in high if there was more action.
 
There's a couple videos of people playing various games on their Macbooks on Youtube. Just do a search for like Half Life 2 macbook or something of the sort. The videos don't really show them doing anything too graphic intensive, but it looks pretty nonetheless! 😀
 
I just found out that Half-Life 2 Deathmatch or Half-Life 2 Episode One doesn't work in BootCamp on my MacBook.
 
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