Transitions between website sections

hi everyone, since im new here i was wondering if you could help with a transition issue that im facing on rigth now.
This is the thing, im designing my first full flash web site, and im basically loading external swf files into a UI Loader for the diferent sections of the website and i need them to have smooth transitions when clicking buttons for the other sections.
What is the best way to do this?

this is the code that im using to call the swf files:

contact_btn.addEventListener(MouseEvent.CLICK, contactClick);
function contactClick(e:MouseEvent):void
{
sectionLoader.source = "contact.swf";
}

can you please tell me how to make this transitions please? should i have to make a transition for each swf or is it possible to use another way? i will appreciate any help!