hi i'm using external CSS and javascript in xhtml and i divided my page in 2 parts (letf and right),i have listed items in left div so if i clicked any item in left's div i want to load it's content in right div.

If I understand it correctly, the left div is sort of a menu and the right div should show the corresponding content. If so, you could do it with hidden divs and a small amount of javascript to 'unhide' the div that needs to be shown.
For an example of the way I do this, look here. This page is still under construction, but the main part is finished.

I found the perfect thing: DHTML.
check that out at http://w3schools.com
It is JS that can redefine any HTML(CSS) in a page.
So you basically use the buttons to trigger a DHTML event which redefines your div.

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