This is what you have.
Make a jsFiddle yourself next time, it will be easier to answer you.
Note that you have an error in a not-closing anchor: <li><a href="#About</a></li>
should be <li><a href="#About"></a></li>
.
I can't get your first question, i already see the parent menu on the left.
For your second question, just remove position: relative
from #mainnav li
rule:
#mainnav li {
float: left;
/* position: relative; */
}
(see demo: http://jsfiddle.net/ZvW9T/2/)
For third question, you are already using jQuery, you can easily achieve that with javascript then, IF it is the way you wanna go.
But mixing css and javascript to generate css creates a bit of confusion in your code, you may wanna re-think the page in pure CSS, following one of the several walkthrough around the web, just google CSS Drop Down Menu .
Please note that, usually, submenus are verticals, not horizontals (sometimes they're mixed, like two columns of vertical values), and that they almost always start from the parent menu tab, not from the beginning of the page...