Well the op said a pentium4 dual core so whatever chip he is looking at the amd is the better choice.
What the op should be considering is the pentium dual cores(e2**0 series allendales) Which peform just about the same as the said amd chip.
Do not listen to anybody that says get a AM2+ plus mobo. That is just a pure waste of money. For a low cost media pc there is no need at all to put a 3800x2 a x2 4000 heck any x2 cpu with the lastest amd boards. Thats like buying a intel x48 chipset to run a pentium 4.
The reason they (and I) suggest the 780G board is because it has the BEST current IGP. This allows you to use a smaller CPU for HD and video stuff. The AM2+ ability is a non-issue. Just search for 780G on google and you will find tons of reviews about how good it is at video playback, many using inferior CPUs (single core and low duals).