There's not a way to playback dvd-a on pc that I know of. However I did find this tutorial on how to rip and convert with some software:
http://www.computeraudiophile.com/content/How-Rip-DVD-Audio-DVD-Video-Audio-And-HDAD-Discs
The software used does convert to FLAC, but costs about $33. There's a freeware program also mentioned but I'm not sure how well it works.