There are TWO different 40GB models of the iPod on the market.
Model #M9245LL/A: 3rd generation release in 2003.
Model #M9268LL/A: 4th generation edition, came out this July
The 4th generation release has:
new longer 12-Hour battery
costs about $20 more
Amazon is currently out of stock on the 4th generation model:
Amazon has the 3rd generation 40 GB model in stock:
The 20 GB Model # M9244LL/A:
The 15 GB Model # M9460LL/A:
Have fun shopping! Good luck!
Call me if you have any questions!
Have a great day!