I need to write a PhoneGap application (with HTML5 and JS, I don\'t need compatibility with IE) with AJAX so that it reads an RSS feed and looks up some specific information
What You mean jQuery can't do XML. jQuery is JavaScript and jQuery uses XMLHttpRequest while doing Ajax calls. See the name XML*. See: http://api.jquery.com/jQuery.ajax/. There is dataType param. You can pass xml to it. After that You will get dom object with all dom object methods.
You can event use it as second param to jQuery's selectors:
jQuery.get(url, {}, function (data) {
var entries = $("entry", data);
doSomething(entries);
}, 'xml');