DECLARE @s NVARCHAR(MAX)  
DECLARE @result INT                
DECLARE @count_me NVARCHAR(MAX)  

/*
The string to be searched.
*/
SET @s = '1101001001110101'            

/*
The character to be counted.
*/
SET @count_me = '00'                    

/*
Replace the character to be counted with empty string, 
and subtract the lengths.
*/
SET @result = (LEN(@s) - LEN(REPLACE(@s,@count_me,''))    )/LEN(@count_me)

/*
Do something with the result
*/
PRINT @result