Hey Bob,
If you're traveling on Rte 9 in Plattsburg(North from the ferry or South from Chazy, I don't know where you're coming from)you can't miss it. There are plenty of signs. Point AuRoche has 2 boat ramps. Drive by the first one and go to the second.
You can probably do a search for Point Au Roche road on mapquest and get more detailed driving directions.
see you there,
Marke