I've discovered that 3.0 and 3.5 are just treated as part of 2.0.  Why they didn't just call it 2.1 and 2.5 or whatever, I don't know, but by selected 2.0 in DNP, a site built in 3.0 or 3.5 will work.

"You'll never see an IIS option for 3.0/3.5 because they are extensions of the 2.0 framework, not new frameworks."