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MS has officially released the DX7 implibs, .h anddocumentation files for download. You can obtainthem from http://www.microsoft.com/downloads/release.asp?ReleaseID=12471
Have a nice life.
I know you probably don't want to pay it, but I'd suggest just buying the CD from Microsoft. It's only like $12.50(US), and then you get all the documentation and whatnot.