他のテーブルの値を使って更新する

UPDATE
  Salary
SET
  Amount
  = Amount +
  (
    SELECT
      (2007 - e.HireFiscalYear) * 1000
    FROM
      Employees AS e
    WHERE
      Salary.EmployeeID = e.EmployeeID
    )
WHERE
  PayDate = '2008-02-14'
  AND
  EXISTS
  (
    SELECT
      'X'
    FROM
      Employees AS e
    WHERE
      Salary.EmployeeID = e.EmployeeID
  )
;

「Salary.EmployeeID = e.EmployeeID」が2回出てくるのがしつこい感じがありますね。