Are you referring to a hook?
Yes. As in the APIHiJack Library.
That's what I figured. Thanks for the link
thread hijack:Right after my last post, I Googled around to try and figure out how this is done. I came across a few places that treated this technique as a scourge, used by hackers to hack running games. Others treated it as a legitimate method. But nothing with source code (though several people mentioned the information was on MSDN which I wasn't able to locate).

I'll Google around for a bit with the API calls in the source and figure out the meat. Thanks again.
I did come across one interesting software project that claimed that it did not use any hijacking at all. Instead, it claimed it brought itself down to the level of the kernel and accessed the GPU directly. But reading the forums and the problems the software had with D10 seems to point to hooking.
Any idea what else could be "lower" than hooking? I'm guessing there's some sort of plug-in architecture on the more recent GPU cards they're tapping into.