You must turn off the Shuffle mode in iTunes if you want to drag and re-order the sequence of the music on your iPod Shuffle.
From a 20-in. aluminum iMac to a 2.4 GHz, 15-in. MacBook Pro (2008) and 2.93 GHz iMac (2009)
From a 20-in. aluminum iMac to a 2.4 GHz, 15-in. MacBook Pro (2008) and 2.93 GHz iMac (2009)