Second the card you listed are better than HD2400pro and 6200 but for HD playback, go with ATI. Take an HD3650 for example.
Depending of the CPU, your can even take an HD34xx.
If your buying a new mobo, you can also take a look of them with a 780G on it. Tom's test it for playback of HD movie with a small sempron 3000+ and it run fine. Considering that chipset had a HD3200 inside, any card in the HD3xxx series should do the job. Your wallet is the limit.