|That's a good start! I wouldn't bother with the GT210, as the HD4000 is faster in 3D. And I'd be willing to bet that a nice fast processor like the 3570k would perform DSP tasks in software faster than a GT210 could in hardware via CUDA. |
I recommend a GTX 560. They should be quite cheap now that the 660s are out, and the 560 easily has enough muscle to make CUDA worthwhile. Plus, if your friend uses a version of Premiere Pro with the Mercury playback engine, that 560 will really get things going.
"Is a separate audio card necessary for video editing?"
No. But if he cares enough about audio quality that he's considering a sound card, tell him to look into USB DACs. A good external DAC will beat the pants off even the best internal sound card. However, external DACs can be pricey, so he'll probably want to start off with the integrated audio.
mATX Beast | LGA2011 i7-3930K @ 4.2GHz | 16GB quad-channel DDR-1866 | GTX 670
240GB SSD+2TB HDD | Asus Rampage IV Gene | Seasonic X560 | Silverstone TJ08-E