Do you have this problem

When i start the starter fps game (the content pack demo1) when i move far from the little forest i saw the tree bottom like big square or rectangle but when i go near they come ok. but in vista i don't have this probleme. do you know how to correct this problem or is just the opengl in linux is to old or i need to update that. i use Ubuntu 7.04
thanks you and excuse my bab english

i forgot if i need to update opengl. wich pack i need to download. i use sypnatic package manager