It is a sequel, but they are making changes to the way hulk and
the movie is depicted from the lesson learnt from the previous
movie (which was a failure).
quote from wikipedia:
The Incredible Hulk is a 2008
superhero film based on the fictional Marvel Comics character the
Hulk. It is directed by Louis Leterrier and stars Edward Norton,
Liv Tyler, Tim Roth and William Hurt. Norton also wrote the script,
after a draft by Zak Penn. Penn said the film is a sequel
to 2003's Hulk, but it will be different enough to also be
considered a reboot. The Incredible Hulk has a target
release date of June 13, 2008.
