$foo = array(
  "life" => array(
    "iwant" => "coffee",
    "ilove" => "caffeine"
  ),
  "work" => array(
    "iwill" => "code",
    "iwant" => "vacations"
  )
);

echo array2xml($foo);

<life><iwant>coffee</iwant><ilove>caffeine</ilove></life><work><iwill>code</iwill><iwant>vacations</iwant></work>