Video skips windows 7

While watching videos on youtube or DVDs the video skips/jerks/freezes about every two seconds. I had no issues with Windows Vista 64, now running Windows 7 Ultimate (64) SP1 on a HP A1510 workstation with the following:

NVIDIA GeForce 6150 video card
Realtek on board sound card

I have done the following troubleshooting steps :
Installed the latest drivers for video and sound card
changed system to best performance
Downloaded VLC