dX10 will be included with the Vista OS, and Microsoft might be holding the rights to produce hardware based on it for a higher dollar amount than usual. Basically, that means Video Card manufacturers are going to have to pay for the source of dX10.
Now, as for what Flerbizky said, I guess there's no real way to tell when it's actual release will be, but if we were going to go with what M$ has done in the past, I'd expect to see it in 4th Quarter 2006. With the exception of XP 64bit, M$'s OS release dates are about 1-1.5yrs after the first beta release.