just get the fastest processor you can that fits your budget, 3500 being preferable. you have to weight out the price to performance ratio and make the judgement call yourself. personally i'd settle for the 3200 on 939 and get assloads of ram, then possibly drop in a dual core in a year or two.
as for the software, you might want to head over to software part of the forum and ask for AMD optimized video editing option.