<?xml version="1.0" encoding="utf-8"?>
<!-- http://blog.flexexamples.com/2007/09/13/checking-to-see-if-a-flex-checkbox-is-selected-before-allowing-a-user-to-press-a-button/ -->
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"
        layout="vertical"
        verticalAlign="middle"
        backgroundColor="white">

    <mx:CheckBox id="checkBox"
            label="I have read and agree with the EULA..." />

    <mx:Button label="Continue"
            enabled="{checkBox.selected}" />

</mx:Application>