You don't really have to watch the first part of Naruto before the Shippuden part, but I strongly recommend you to watch it.
There are several reasons of why you should watch the first part (or at least read the manga):
- Character development:
You will start by following the characters since their first days in the academy, and you will start to watch them grow every episode, you will know their life, their personalities, love some, and hate some, you will understand them and how they feel toward each other, and witness every single piece of event that made them arrive to what they are in the Shipudden part.
- Grow in strength:
Starting by the first Naruto part will make you start by seeing the beginners ninja techniques, you will start by seeing that creating a clone is a huge achievement ! And after long episodes and long days of training/fighting, you will start to see the development of each ones techniques and feel the value of it even if it's still small, and that's the most important part in every anime: character development, precisely for this part: the growth in strength (physical and mental). By starting with Shippuden you will start already by large techniques, strong characters, big fights.. and that's not that cool as a start.
- The Story:
Of course if you skip a part of the anime, you will skip a part of the story, precisely the childhood of the famous characters (and it was the fun part of the story, since Shippuden is a part of war).
There are several other points that you can miss by skipping the first part, but as I said first, it's not that you can't watch Shippuden directly, it's that it's better for you to grow with the characters since their first days.
There are many people who wish to lose their Naruto-memory so they can watch it again, you still didn't watch it ! don't waste this chance : )
