hm, how many shader processors does this onboard thingy have? because i very much doubt that you will be able to play back 1080i content on a single core processor without heavily compromising quality.
to get good deinterlacing, you will either need lots of shader-power and VA-deinterlacing from the ATI chip, or you are lucky and have a good TV-display with e.g. a faroudja deinterlacer.
you should be fine for blue-ray, however.
Toms hardware has an article about the 780g chipset you should check it out. They ran test and were able to play HD content with a Sempron 3200+ (I think). Regardless of what processor they used it was a single core, with a duel core you would be more then capable of playing 1080i which is what I plan on doing soon as well.
Germany