select min(salary)
from (
  select top 4 *
  from employees
  order by salary desc
) as a

Select top 1 salary from (select top 4 salary from tbl_emp 
order by salary desc) temp_tbl order by asc

For Finding Nth Salary...

SELECT TOP 1 Salary FROM
(SELECT TOP nth Salary FROM Table Order by Salary Desc)Table
As Sal Order by Salary

select salary from employee aa
where 4=(select count(*)from employee bb
where aa.salary<=bb.salary)

if you have a table emp and you have to find fourth maximum 
salary from emp table then you will have to write this 
query.....

select top 1 sal from (select top 4 * from emp order by sal 
desc) as sal order by sal