You can easily deal with AlloyUI in Liferay 6.2. You need a placeholder for the progress bar - something like this:
<div id="myProgressBar" style="width:100%;height:20px;"></div>
And then you can create it using javascript as follows:
<aui:script use="aui-base,aui-progressbar">
var progressBar = new A.ProgressBar({
boundingBox: '#myProgressBar',
label: '<%=percentage%>%',
orientation: 'horizontal',
value: '<%=percentage%>',
}).render();
</aui:script>
You can find out more about the configuration settings of the progress bar here:
http://alloyui.com/api/classes/A.ProgressBar.html
And some examples here:
http://alloyui.com/versions/2.0.x/tutorials/progress-bar/
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