Unlike the iPod Touch Porn Videos, iPod Nano Porn Videos have to be downloaded and then sync'd to your iPod Nano using iTunes.
This really isn't a problem. In fact you should count yourself lucky that you'll never suffer the disappointment of the porn provider screwing up the video encoding for QuickTime streaming, or your wi-fi connection packing up half way through a porn movie :)
The only thing you need concern yourself with is whether your chosen porn service has made their porn movies available in an iPod Nano / iTunes friendly format.
Should you opt for a porn service that hasn't taken the time to make the movies iPod Nano compatible in QuickTime, your iTunes software may convert downloaded video files to a friendly format and transfer them to your iPod Nano, but you'll need to check with them first.
Essentially, you just view the porn site using your Mac/PC, download/save the porn video to your hard drive and then sync it to your iPod Nano using iTunes.
