HD5570 is still $75-80. Even onboard graphics can handle what he is asking about. I guess he could go for an HD5450 for something newer but unless he will be bit streaming audio to a receiver I don't think it matters much.
Should i buy 512Mb or 1Gb Ati Radeon Graphic Card ?
Yes, you are right jyjjy, the OP isn't gaming at all, so HTPC card like HD5450 is just enough...