Background;  Who are the Nameks?

Unlike the Saiyans, the Nameks are by nature a peaceful race (Piccolo being the acceptation).  Their home planet is, or was until like Vegeta, it was destroyed by Frieza.  The Nameks were the people who created the Dragonballs.  They are all one sex, and although it says in the series that they are neither male or female, I tend to think of them all as males (otherwise I tend to get freaked out).  They do not need food to survive and live on water.  Because they are all one sex, they reproduce asexually, but they are all the children of Guru, the eldest Namek (again, this tends to freak me out).

Where do they come from?

The Planet Namek!!  Don't you people listen?!  The planet Namek is millions of light-years from earth.  The planet is a lot like earth in appearance and stuff.  

So, how did Piccolo end up on earth?  I take it he wasn't sent to destroy it too.

Kami crashed to earth in his ship when he was a young Namek and couldn't get back.  He created the dragonballs on earth and stayed to become the Earth's guardian.  For details see characters and the Piccolo profile.  In short, to become the Guardian of the Earth, Kami had to rid himself of all the evil with in him.  So he separated into two.  The good Kami, who would become 'God', or 'Guardian of the Earth', and Piccolo Daimao (or King Piccolo in the dubbed versions...typical).  Piccolo Daimao was the embodiment of everything evil in Kami.  Piccolo Daimao tried to take over the earth and was defeated by Goku (in dragonball when Goku was a child).  Before he died, Piccolo Daimao created an egg.  This egg was to hold Piccolo.

They can I say this...weird!

Hey, just because they are all quite physically big with large muscles, bald heads, antenna and green skin that's no reason to get all judgmental!!

Who are the Nameks we see in Dragonball?

We see a lot more Nameks than Saiyans, but these are some of the more important ones (at least as far as the storyline is concerned).