[Fish Horse]

Hi,

I had the same problem. The NVIDIA GeForce GT 120 doesn't handle ProTools + video very wel. In particular combined with HD cards there's a bandwith and/or memory problem I think.
We switched to ATI Radeon HD 5770 to drive 2 PT screens via DVI. Video out through a Blackmagic Design intensity Pro hdmi to flatscreen (200$). This combination works very good.

Strange enough, with the home rig (no HD core and accel card and no BM Intensity), video plays very smooth with the GT 120 connected to an old LaCie monitor (via DVI-SVGA adapter). ATI Radeon HD 5770 here as well, to drive 2 flatscreens.
If you want to use just one display for PT + video, I think the GT 120 is too light.
FWIW motion jpeg works best here. We convert with MPEG streamclip.