create function dbo.varchartovarbin( @string varchar( 8000 ) )
returns varbinary( 100 )
as
begin

declare @i int, @val binary, @result varbinary( 100 ), @length int

set @i =  3 
set @result =  0 

select @length = len(@string)

 -- validation of params
 
if @length < 4  or @length %  2  <>  0   or substring(@string,  1 ,  2 ) <> '0x' or @string is null return  0 


while (@i<@length)
begin

select @val = 
      (case substring(@string, @i,  1 )
       when '0' then  0 
       when '1' then  1 
       when '2' then  2 
       when '3' then  3 
       when '4' then  4 
       when '5' then  5 
       when '6' then  6 
       when '7' then  7 
       when '8' then  8 
       when '9' then  9 
       when 'A' then  10 
       when 'B' then  11 
       when 'C' then  12 
       when 'D' then  13 
       when 'E' then  14 
       when 'F' then  15 
       else - 1 
       end) *  16 
+
       case substring(@string, @i+ 1 ,  1 ) 
       when '0' then  0 
       when '1' then  1 
       when '2' then  2 
       when '3' then  3 
       when '4' then  4 
       when '5' then  5 
       when '6' then  6 
       when '7' then  7 
       when '8' then  8 
       when '9' then  9 
       when 'A' then  10 
       when 'B' then  11 
       when 'C' then  12 
       when 'D' then  13 
       when 'E' then  14 
       when 'F' then  15 
       else - 256 
       end

  set @result = @result + @val

  set @i = @i +  2 

end

return @result
end
go
select dbo.varchartovarbin('0x1234')
go