That initial report pegged the new iPod's display at 3.5-inches, but reliable sources say that after considering both 3.5-inch and 4-inch prototypes, Apple has settled on the larger iteration for production.
The new iPod remains on track for an announcement possibly as soon as late March or early April but sources caution the roll-out could be pushed back pending an agreement with the movie industry on distributing feature-length content. Apple is said to be looking to launch the first movie content for sale on the iTunes Music Store in tandem with the new video iPod, capitalizing on the joint publicity each would garner while offering a clear incentive for early adopters to purchase the new iPod.
Apple's new iPod to have 4-inch display

According to ThinkSecret, Apple's new "true" iPod video will feature a 4-inch display with a quarter-inch border. The device will feature the dimensions of previous iPods but will have a much bigger display: