Use the noConflict method for jQuery and assign it to a new (short) variable. Use the new variable wherever you would have used the $ for jQuery.
var $j = jQuery.noConflict();
$j(function() {
$j('#selector').each( .... );
});
or, if you don’t need to mix Prototype/jQuery you can wrap all of your jQuery code in an anonymous function.
(function($) {
// $ sign here is a parameter, which is set to jQuery
$(function() {
$('#selector').each( .... );
});
})(jQuery);