I’m actually having the same problem. Not using HDV but it seems any video is jerky and slow to play or scrub. First I used a 5-sec AVI file and it was terrible. Other formats yield the same results. Then I tried sequenced PNG files and the same problem albeit slightly better but still too poor for workflow.
Not sure what the problem is but I’m running Windows XP64 SP1 which still has plenty of bugs in it on a robust system.
Digital Fire Studios
Precision Homebuilt: Asus P6T Deluxe V2, Core i7/920 OC-3.4GHz, OCZ 12G DDR3 RAM, Nvidia GTS250 w/1G DDR3, 3.2 TB, LG Blu-Ray/HDDVD RW. Adobe Creative Suite CS4, Sony Vegas Pro 8, Particle Illusion 3