Is there a difference between potassium manganate and permanganate? Is potassium manganate the same as potassium permanganate?

Also, I have seen potassium manganate written as potassium manganate (VII) or potassium manganate (VI). 

What do the roman numerals stand for?
No, they are somewhat different. $\ce{K2MnO4}$ is potassium manganate and $\ce{KMnO4}$ is potassium permanganate. Notice the two potassium for each $\ce{MnO4}$.

The Roman numerals mark the oxydation state. So, manganate will have a (VI) and permanganate will have a (VII).