WordPress and $_GET Params

For custom parameters you should register them with WordPress:

add_action('init','wpse46108_register_param');
function wpse46108_register_param() { 
    global $wp; 
    $wp->add_query_var('anyParamName'); 
}

Then the value of ‘anyParamName’ can be found with get_query_var

$anyParamNameValue = get_query_var('anyParamName').