what exact model?
a mx440? a geforce 4000?
nvidia tends to support their video cards for alot longer than amd so probably still supported with the right driver from synaptic
maybe the question would be if it is still a good idea to keep using it and what kind of use you want to give to it under kd4?
if light effects and normal usage like flash videos, 720p videos and some casual games, probably will be just fine
it all depends on the specific model and if the driver still exist for it
now, about the livecd and the problems, you could be a bit more specific about the problem and maybe we could try to force it to load a vesa driver to load gui and from there load another nvidia driver