i play on cro sakura server,which is free and legal. the thing is registration closed so you = teh fucked :| but i think thats the server you were talking about >_>
the thing about private servers is there normally about 60 to 100 people on but they normally boost the exp so you get 10x/10x or around there and they boost the item drops aswell,so its less hard to level and get rare items D:
also,all the private ones ive played on, most of the GMs = assholes so its extremly hard to get in unless if you know their friends or are their friend and so on >_>