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Erg, I hate repeating myself, but its a sad fact that the half life game is made using the quake1 engine (very heavily modified) and not the quake 2 engine.
Many people get this wrong simply because Half life uses opengl a lot more than quake1 did. But its a fact. For proof look up the ID technology's licencing information page.
*sigh*
Ah, ok.. I recall all about that debate now. I've made note of it in the post. tah. [:)]