I would take my cue from the minimum hardware specs of the editing software you wish to use as they vary
A decent dual core Pentium with min 1Gb of RAM and a Video card perhaps with own ( not shared) memory would be a good starting point.
I would really just buy the most powerful you can afford as even with software, they tend to quote minimum hardware spec ( often a little optimistic) and recommended specs ( more real world!)
Besides you never know what future format is round the corner.. get something with a little grunt and keep

ing for a while