Also: what is the heighest, and what the lowest rank ?

you do good in games, i think politcal puppet is the lowest, and diplomat at the highest

All about points available, I believe.

that would make sence

No, it isn`t i was also an political puppet when i had 130 .
Also this would be really unfair because then any newbie can come, win his first game an d have a better rank than a player that has won already 10 games, but always sets his points into more games.

Its about rankings. Rankings is based on the # of points you have:
http://vdiplomacy.com/halloffame.php
So cause Bozo as 1300 he is ranked first, cause Roxart has 700 he is ranked 2nd etc etc.

There are currently 196 'ranked' players. AKA players with more then 100 . To calculate your ranking you divide your ranked (in my case at #87) by the 196. This givers you your ranking %. Again using me as an example we get 0.45. If that number is over .9 your ranked a political puppet. If that number is under 0.05 your ranked as a diplomat (I forget the rest of the list). So its not based on points, but the number of points you have compared to everyone else.

So I have to have many points ?

Top 5% seem to be Diplomats
5-10% seem to be Masterminds
10-20% seem to be Pros
20-50% seem to be Experienced

~1200 registered members and ~200 with >100 available points? Wow. Considering the fact that the system won't let total points drop below 100, there are ~1000 people on this site playing games with so few points that buy-ins take them under 100?

Or people quit the site, CD, and sit at 100 after being restored.

I'm the most time under 100, why i don't should spend my points ?