IPod

Playlist on the Mac or the iPod?

 

By "dimmed" do you mean ''greyed out"?

Because that would mean you have your iPod set to sync automatically. Thus when you change your iTunes library the iPod is updated automatically with those changes.

If you want to play songs directly from your iPod you have to set the iPod manually manage your songs. You do this in the iPod summary window in iTunes.

ps. "iMac" and "iPod", not IMac or IPod.