Align Center with fix width entire theme

Hello everybody!
I am new in gallery2 installation and customization. I am very excited about this gallery.
I want to align center entire site (theme), with fix width. My banner is about 1000px, and i want to
entire theme to be 1000 px.
What should i modify and where?

This is my gallery:

www.pirvulescu.ro

Any sugestions will be apreciate.
Another problem, (but first is very important to me) is to figure out how can i add that beatiful shadow.

Thank in advance,

Yours sincerly Edmond