I just found a website (http://news.softpedia.com/news/DirectX-10-Available-Outside-of-Windows-Vista-53066.shtml)
that has a link to a download that allows you to use DirectX 10 on OS's other than Vista!
"I'm proud to release a preview of our DirectX 10 compatibility libraries. And the operative word is PREVIEW.
To me, the persuit of DX10 is moot, because I have no application installed that uses it, including FSX.