I know it's a bit late, but if it helps:
I have a Shimano 7-speed hub (it came with the bike and it's brilliant). Although braze-ons will give a neater result, there are no 'bits' actually required between the shifter and the cassette unit (which should come with the hub, and fits over the axle inside the dropout). The cable (ordinary Shimano brake cable) runs completely enclosed from one to the other - all you'll really need is a few cable ties to keep the thing in place.
The Shimano Nexus range includes a couple of different shifters, integrated with brake levers or separate. Look at the Shimano site for details - http://cycle.shimano-eu.com
then do a product search for 'nexus'. You might also want to look at the more recent Nexus 8-speed hubs. I would.
Of course, all this assumes that the gap between your drop-outs leaves enough room for an internally geared hub: the Shimano site details the necessary measurements. And also that the drop-outs themselves are not vertical (unless you're prepared to use some sort of chain-tensioning device).