Hello all. My current PC is running off an old X2 3800+, 7900GS, M2N-E motherboard, and 2GB of DDR2. Now, I've been getting into 3d modelling and video editing and such, so I was looking into upgrading my CPU.

My question is, should I go Intel (meaning I would have to buy a brand new motherboard and possibly reinstall windows... Which I'd really rather not do), or would I be alright going with an AM2 phenom?

I was looking at the new quad core phenom 9850 black edition, what would you guys suggest? Or will this motherboard even support this processor?

get x2 6000 or 6400

or build a new pc

If you have the option (spelled $$) to go with an intel C2D or CDQ  and a new motherboard you'll definitely see a performance increase and have a chance for great overclocking.  A Q6600 would likely set that video editing free, but you have to pay to play.

AMD is not a 'top' performer. I'm not a video editor guy so I don't know what all it involves as far as processor load but Intel all the way for faster performance and more overclockability. phenom isn't really worth it and your mobo probably doesn't support it because your currently sporting a weak 3800+. I suggest you check the CPU compatibility list for your mobo and pick up AMD's best chip, the 6400+ if supported, otherwise might as well convert over to Intel.

I did, every processor before getting a 2160(2 months ago swapped it out for my current after a month)was an AMD, back then they did their job and did it well enough, but when it was time to upgrade my X2 3800, Intel was the obvious choice for price/performance and still is.  
 
When AMD has a CPU that competes price and performance i wouldnt hesitate to consider them, until then I'm sticking with Intel

Just checked asus' support list for my motherboard, and it does support the new phenom CPUs (both X3 and X4), would you still suggest going with a weaker 6400?

not weaker

 
If you will be doing video editing / encoding using software that has more than 2 threads you would be better off with one of the phenom processors. If you're going to be playing games a lot then at the moment the 6400 X2 is the better deal.