Q:

How to convert value to specific date?

I need a sql script that can convert value to currents months date, that for example if i pass 26 then it will display 03-26-2011  or convert the 26 to system date of current month and current year and so on. 

A:

dateadd(month,datediff(month,0,getdate()),0)-1 + 26

The +26 at the end is what makes it the 26th of current month
As a function
create function dbo.DateForDayOfCurrentMonth(@daynum int)
returns datetime
as
begin
return dateadd(month,datediff(month,0,getdate()),0)-1 + @daynum
end
GO

Example usages:
select dbo.DateForDayOfCurrentMonth(26);

select dbo.DateForDayOfCurrentMonth(numbercolumn), ...
from tbl

