To be fair, unless you plan on doing other computer work at the same time then almost any card will suffice. A lot of people will tell you to get a Radeon, but I see little difference between ATI decoded DVD and that done by my old Voodoo5, or GF2mx(with PowerDVD3/WinDVD). I think that if your system is fast enough then all you'll need is a TVout. ATI fans appear to be clinging on to the DVD playback thing as their last hope of Radeon being better than any other card(something that is totally unfair), or maybe just to justify their purchase ahead of the equivalent Nvidia card. 
 Alternatively you could just buy a dedicated DVD decoder card for about $30 and have even better quality still and DD5.1 as a bonus!