Hi David,
I'm sure the DVD-Audio version of 'Say You Will' will be available in stores, since the 'Rumours' DVD-A was, but your safest best is probably ordering it from Amazon.com.
They're selling it for $14.99 (list price is $18.98), and shipping is free if you have an order of $25 or more.
You can access their page, by clicking here:
'Say You Will' DVD-Audio at Amazon.com.
DVD-Audio discs will play in
most DVD players.
The second disc of the Limited Edition version of the album, will apparently contain "Not Make Believe," "Love Minus Zero/No Limit," "Peacekeeper (live from AOL Sessions)," and "Say You Will (live from AOL Sessions)."
There's a possibility that those live performances of "Peacekeeper" and "Say You Will" are solely video-content, and are not also on the disc as seperate audio content.
As far as "Peacekeeper" being released as a single... it's rumoured that a CD-single will be available in Europe at some point, but there's been no confirmation on that as of yet.
It's highly unlikely that it will be released as a CD-single in the US.
Hope this helps!