Right, then. According to http://en.m.wikipedia.org/wiki/IPod_Classic#5th_generation that iPod came along in 2005, was the last one with a plastic cover before aluminum bodies came along.
From Apple:
iPod (5th generation Late 2006)—also known as iPod with video or Fifth Generation iPod
You can distinguish the iPod (5th generation Late 2006) from the original iPod (5th generation) by the last three digits of the serial number. The iPod (5th generation Late 2006) serial number's last three digits will be one of the following: V9K, V9P, V9M, V9R, V9L, V9N, V9Q, V9S, WU9, WUA, WUB, WUC, and X3N. The Fifth Generation U2 Special Edition iPod (30 GB Late 2006) serial number's last three digits are W9G.
iPod (5th generation)—also known as iPod with video or Fifth Generation iPod
The iPod (5th generation) is a a hard drive-based iPod featuring a large, widescreen color display, a Click Wheel, and the capability of displaying photos and videos. Like iPod nano, it uses USB for syncing and comes in white and black.