As you probably know there is a manga and an anime about Naruto. The anime is based on the manga. Although the anime stays very true to the manga, there are some small differences between them. The Anime vs Manga section will tell you all about the differences we were able to find, this section will regularly be updated as more differences are found.
Because the anime is based on the manga, the story is a lot more ahead in the manga compared to the anime's. Altough they "had" to air more then a full year of fillers because the anime was closing in on the manga in 2005. Basically the manga's story advanced, while the anime went on a filler spree mid 2005 until begin 2007. The anime only picked the main storyline back up with the second Naruto installment, called: "Naruto Shippuuden". The manga is still running, so who knows how long the series will continue?
Neji's mark on his forehead looks a little different from the one shown in the manga. In the manga the mark looks more like a swastika. Most likely it was changed to make the series more accessible, you never know how the younger viewers' parents will react. The symbol is most famous as "The Nazi Symbol" after all.