This has been probably the hottest topic in this forum, and now, as I had promised, I have the video posted with the "bottom line" explanation of why the Intel 915 integrated graphics solution doesn't have a WDDM driver.
Go watch this video on the Intel Software Network blog, that I shot with Intel's Chuck DeSylva at GDC 2007 a couple of weeks ago.
The short version (if youre impatient): The WDDM Vista driver spec
came out long after the 915 design was complete and in production, and
even though it has advanced features like Pixel Shader 2.0, there is a
missing hardware feature, called the Hardware Scheduler, that 915
lacks, and without that, it doesnt meet the WDDM spec from Microsoft,
and we (Intel) cant release a WDDM driver for it.
There. Its done. I hope that answers your questions. Please link
your friends and associates to this video/post for the definitive
answer. I know this isn't the answer that most of you wanted to hear, but we're being honest and transparent here, and unfortunately, this is how it is.
As always, let us know if you have more questions! Post here in the forum, or leave a comment on the blog post - that's the best way to reach us. Thanks!