First build - I need help

I have been doing research for some time on doing my first build. I am not a hardcore pc gamer but I want a computer that I can burn dvds fast and efficiently, while being able to do other tasks too (i.e., run mozilla, media player, bitcomet, etc etc)

This is going to be a huge upgrade for me regardless (considering I am running on an obsolete celeron single processor with 256ram)

I was looking at the high end of AMD's 64x2 (6000 or 7750 black) as being sufficient for me but I don't know.

I just really don't know what is going to be best for me.

I am also having trouble choosing a gpu. I have had my eyes set on the ATI HD4850 as a general idea price and performance wise.

DDR2-1066 - 4 gigs or more (plan on running vista64)

I would like to keep this computer under $500 - $600 without the gpu.

I hope that's enough information to get some good feedback.

Thanks