It can be done with Seapro but I think that is using a full new system and I think Raymarne had a box to work with their nav software. I've seen a few other products out there but they are not aimed at the leisure boater. If anyone knows otherwise, I'd be interested too.
Thanks for your input. Had a look, but expensive!!
I was hoping for software which would use output from existing radar dome or even as a repeater, from existing radar unit.