preview to NTSC

Does anyone know of a tool like I had with Media 100 where a small app can be run in the background where:
You have a movable frame on your desktop that is the size of a video frame (720x480 for DV), it takes a snapshot of that frame every few seconds and sends it out to your NTSC video out. The Media 100 version obviously sends to the Media 100 hardware.
I want a tool to send this out to firewire video device for previewing designed graphics on NTSC monitor. It's so simple and so useful, I can't believe I can't find one for firewire and preferably OSX.
thx
pd