Center components inside the hole application

Hi experts,

Since i can't design my own components using SDK, because if this problem Re: Error importing developed SDK into DS 1.2

I'm trying to do what i can with the native components of DS 1.2, and i can't figure out how to center all components on a page.

As you can see in the image bellow, all of them stay in left, and i wanted them to stay exacly on the center, so when the user resizes the page, or has a different resolution than i do, it wont be a problem.

And another layout question, how do i define the size of my application, lets say i wanna it to always be 800x600 px.

I'm just begining , so i'm sorry for the silly questions.

Best

Leandro