Still getting used to hacking at these forms.
Here's some code to get started (see the documentation at
http://developers.marketo.com/documentation/websites/forms-2-0/) for where to put this.
function(form){
$("form.mktoForm").attr("style","width:100% !important"); //You may want to declare a fixed width in pixels; that's ok too. This overrides the font style added to the form so you may need to declare it elsewhere.
$("label.mktoLabel").hide();
$(".mktoForm .mktoFormRow").attr("style","clear: none; float: left;");
});
There is still a lot of stying that would need to be done, but this gets you on the right track. Find me on LinkedIn if you need more personalized help/consulting.