http://crmdm.blogspot.com/2011/06/how-to-retrieve-lookup-attribute-from.html
Code Snippet:
var lookupObject = Xrm.Page.getAttribute("yourlookupattributename");
if (lookupObject != null)
{
var lookUpObjectValue = lookupObject.getValue();
if ((lookUpObjectValue != null))
{ var lookuptextvalue = lookUpObjectValue[0].name;
var lookupid = lookUpObjectValue[0].id;
}
}