Do any of you know of a high quality low latency video capture card?

I currently display cameras, DVD, VCR and PowerPoint on two projectors and 3 TVs. To do this I use a scanner to convert VGA to CV and then feed all CV signals through a CV mixer, to a CV distribution amp and hence to the projectors and TVs. However I want to increase the quality of the image. The majority of the time is used to display PowerPoint and the projector screens cover many more people than the TVs. So I would like to have a VGA signal direct from the PC to the projectors. However I still need to allow for the other CV (or sometimes S-Video) signals to display on those same projectors. Changing the input source of the projectors (between VGA and CV) is akward and slow. It seems to me that a video capture card could be a solution, however as the screens can be seen at the same time as the action being filmed by the cameras, there needs to be no noticable delay between the CV signal going into the card and the VGA signal coming out of the PC.