for all my previous vids iv used a standard mini dv cam and sony vegas 7.0, and that was fine, but recently i was thinkin about upgrading to hd cam and sony vegas 8.0 so i downloaded and installed vegas 8.0 and got sum clips off a frend in hd form, to hav a play and wehn im editing them, the preveiw screen is really jerky, like misses bits out, so i wondered if it was the new program, i imported sum standard dv clips and the preview screeen was fine, but its when im editing them and trying to preveiw my progress, the little preview screeen is really jerky, why is this? do i need a new graphics card? i also rendered the hd footage afterwards and was fine, jus cant see what im doin whilst editing it, because the screens so jerky what do i need to do? any help appreciatted