I have AMD 64, 3000 With 1 Gig RAM , 2 X 300 Gig serial ATA drives
Sony Vegas 6d with Sony’s HDR-HC1 and it captures and plays back HDV smooth, your computer configuration seems to be a lot faster than mine.
have you tried defragmenting the drive( where the Video is stored )???
has to be your computer, I would also check Vegas preferences—video— playback options and trying switching from best to Auto and see if it makes any difference.