Loading scripts with ScriptMangerProxy not finding page controls since update to RC1

I have recently updated my AJAX to RC1 and some pages that load js in the scriptmanagerproxy have stopped working...
The problem is that when i try to get a text box it doesnt exist...

$get("txtFirstLine").value

...this is not in a function its just in the file but the object is not found.
It will work i wrap it in a function and call that function at the end of my aspx markup

<scriptlanguage="javascript"type="text/javascript">firstfunction();</script>

...its like the js is now all executed before the aspx page and controls on it are created.

Is this is the case?
Is there an event in the AJAX library that i can use to run this script once the page has been created?

Thx
Steve

You can take a look at theSys.Application.init andSys.Application.load events in the doc.