nVidia and KDE 4


I have installed nVidia 7300 GT in my comp, after installation oS 11 I have got some strange behaviour. I have 2 user accounts both use the highest screen resolution. But on one of them when I loggin I have splash screen and after loggin I have got normal desktop view. But on second account after loggin I have got a black screen only with a mouse. When I wait a little time and press Alt+Ctrl+Del I have got normal screen with option to log out or shut down or restart. I press Cancel and can work normally.
But what is the problem that I can see this black screen and how to fix it?
The second question is how to change my screen resolution under oS 11 I can only get 1280x1024 but under Win XP i can get 1600x1200. How can I fix it too?