When I connect either one of my iPods to iTunes (yes, using Windows so save the Mac / Apple preaching), select the device - all the music is grayed out.
When I search for a solution, I see tons of topics regarding the same issue but with a "Stop" / "Circle" next to the songs. I am not having that issue. I can still play the songs from iTunes but can't drag / select songs through the actual device.
And yes, you can all clown the songs in the screen shot... ***holes.
To be serious for a minute, I'm assuming you're unable to change out the music on your ipod? (And I can see why you would want to.)
It's not a solution to the grayed out problem, but I have used SharePod with a ton of success on an ipod I found a few years back. Skips all the useless steps itunes forces you to go through to change music. It's a real drag/drop Windows-type interface that's really easy to use.