[javascript] How can I use jQuery to move a div across the screen

In jQuery 1.2 and newer you no longer have to position the element absolutely; you can use normal relative positioning and use += or -= to add to or subtract from properties, e.g.

$("#startAnimation").click(function(){
    $(".toBeAnimated").animate({ 
        marginLeft: "+=250px",
    }, 1000 );
});

And to echo the guy who answered first's advice: Javascript is not performant. Don't overuse animations, or expect things than run nice and fast on your high performance PC on Chrome to look good on a bog-standard PC running IE. Test it, and make sure it degrades well!