Half Life 2 will not run?

I have a black Macbook 2.0 Ghz with the GMA 950 chipset(if that helps) and 4 gigs of RAM. I put an XP partition on my computer and after reading about various peoples' successes running Half Life 2 and other games even on computers with lower specs than mine, installed Steam and subsequently HL2, Counterstrike Source, and DOD Source. However, whenever I try to run them, I get a small window with the Valve logo screen, then the copyright screen, and then it quits. The hl2.exe program is actually running as I got the dialog box asking me if it should be allowed to run from the Windows Security Center. I had read that such a problem might be due the fact that my integrated video uses RAM, and that not enough RAM was allocated to it. I had also read that it might be due to a driver issue of some sort, but after repeatedly reinstalling drivers I'm fairly sure it isn't. I also have tried using the launch options to set the DirectX to 8.1 and even 7, and had no luck. Can anyone confirm that it's a video memory problem or maybe make another suggestion as to what to do? I'd really appreciate any help anyone could give me.