Template and dynamic classes

[eluser]Radou[/eluser]
Hello everyone.

I am using a template with header.php, sidebar.php, main.php and footer.php
On the sidebar panel I have menus organized such as :

Code:

<ul>
<li class="active"> Test 1 </li>
<li> Test 2 </li>
<li> Test 3 </li>
</ul>

I don't want to load the sidebar everytime, but when I click on the menus I want them to change class to "Active" and remove that class from the first <li>

My question is actually devided on two :

1/ How can I change the class dynamically on click
2/ How to load the main view without loading the page (ajax ?)

Thank you