Pirates of the caribbean,good game,but one thing ruing it all!

[Timmtimmy]

hey everyone,Pirates of the caribbean(single player ^_^) is my favourite game,really love it so much(I know there are few games of about same name,but I mean the one where you start at Oxbay hehe)
So I tought to give Pirates of the caribbean online a try,and I can say I love it really much!
But there's one problem ruining it all.
My pc:nvidia 7600 GS,1gb of RAM,amd athlon 3000+
Isnt nothing special,but I suppose its at least able to run the game at medium with around 25 fps?
But what do I get?I get sudden fps downs quite often,not so much on the land,but mostly on the sea,and ALWAYS when Im on someone elses ship and/or boarding the other ship.
Could anyone please give any suggestion?:/
I really like this game and I wouldnt like not to play it because of this.
I've played World of Warcraft wich requires stronger pc without any problems at all,so Im quite confused why Im having problems with this game,wich is,by the way,alot better than WoW =D