Best way to get to New Gourna is by bike from the West Bank of Luxor. Hire the bike on the west bank: a day's bike hire there should cost the same as hiring a bike on the other side of the river but the bikes on the Wets Bank seem to be of a much better quality (i.e. newer). Not that you don't need to check them thoroughly.
It's a ten minute ride on the main road West.