I'm not sure if your plan will work. I have two video cards right now running dual monitors, a Geforce3 and a 3dfx Voodoo3 3000 PCI. When I use PowerDVD to watch movies on my primary adapter, the Geforce3, everything works like normal, but if I try to drag the video window to my Voodoo3 adapter/monitor, then window just goes black. This leads me to believe that you may not get DVD video out of your secondary adapter either. I think it just has something to do with which card you set as your primary graphics adapter. Then again, I could be completely wrong, and your idea may work flawlessly.
Edit
Wait, do you want to run the setup kind of like a dual monitor setup where you can drag windows from one display to the other, or do you just want to have the displays mirror eachother. Also, does it really matter what resolution the second adapter is set at since you're planning on outputting to a tv, and tvs only display a resolution of 640x480?.....unless of course you have an HDTV.