Thanks for your help firs of all... And please be sure that the twitter widget you see now, is not the widget that causes problems before. They have the same interface, but they are not the same software. So it is not suspicious as you guessed.
Your codes worked well. Thanks for that. But if you read the message I wrote above, you could see that the problem I have is not only the equalizing the distance between menu items.
Please have a look: http://imgur.com/jGcri
You can see the submenu is nested with menu it belongs. So how can I resize the distance between the items oof first menu? When I want resize them by giving a value more than 10px there would be problem in submenus of first menu as you see.
Please claw this issue and fix. I trust you. You can do that.
And also I wanna ask that the codes Ismael and Devin gave above, must they added to style.css or style4.css which I use? I added them to style.css because they wrote like that.
PS: I am awared that I wrote many issues, may be this may bother you, but I want to fix my problems step by step, one by one. The remaining problems I have, are not so difficult as you see before, please take it easy.. :)
PS-2: I want also the codes of Ismal's and Devin's, working form for my site.