I recently installed a Nuvinci and a SBP shifter kit on my Micargi "General" cruiser. There was a little bit of work involved in the hub installation, so I took some pictures and I'm describing the process here.
Step one - find the Nuvinci hub and a freewheel. You can find the whole wheel (already laced-up with spokes and everything) here: Amazon.com: Sun Rhyno Lite XL / NuVinci Nuvinci Gearless 26 x 1.75 36H Black/Black: Sports & Outdoors
, but I found it to be cheaper to get the pieces individually. A couple of web sites have these hubs significantly cheaper than most: Tree Fort Bikes Online Bicycle Shop - Mountain & Road Bicycles | Repair & Tune-Up Sales in Ypsilanti, Michigan near Ann Arbor
and Motorized Bicycles Detail Page
. (There are probably other good websites, please chime in if you know of any). Then look for an english-threaded (not metric!) 16- or 18-tooth freewheel to put on the hub. I found my freewheel at a local bike shop, I'm using a 16-tooth. Then lace your hub into a wheel.