I got my rtfm right the second time.
Get yours here.http://ftp.heanet.ie/pub/linuxmint.com/ ... nglish.pdf
I found it is necessary to follow the instructions pages 16-18.
Simply allowing the installer to decide how to re-size existing partitions does not work, at least for dual-booting.
Some of the options are different than the screen shots in the user guide.
I made both my main and swap partitions primary partitions.
If you indicate type as swap, it knows it is supposed to format that partition as swap and where it's mount point is supposed to be.
Now all is good.