1. Go to your Advanced Search Page.
   
2. Edit the Page.
   
3.  Expand the Scopes portion of the menu.
   
4. Check the box "Show Scope Picker."

Now you can check the box to keep advanced results in the scope(s) you choose.

To preselect all check boxes:

1. Go back into Edit mode.
   
2.  Add a Content Editor Web Part to the page. 
3. Set the Chrome Type to "None" (this hides the CEWP).
   
4. Open the Source Editor and enter the following script:

<script type="text/javascript">

_spBodyOnLoadFunctionNames.push("checkAll");

function checkAll() {

    var frm = document.forms[0];

    for (i=0;i<frm.elements.length;i++) {

    if (frm.elements[i].type == "checkbox") {

    frm.elements[i].checked = true;

        }

    }

}

//-->

</script>