You can specify an xml datatype in your get request. The data object will then be the XML root element:
$.get('PathToLocalXmlThatIUsedPhpToDownload', function(data) {
//work with xml here
}, 'xml');
It's probably more efficient to work with the XML directly, rather than converting it to a javascript object and then working with the data. However, if it makes more sense in the context of your problem to use a javascript object, see the answer to this post: Tool (javascript) to convert a XML string to JSONTool (javascript) to convert a XML string to JSON