Strange Difference Between Sql 2002 And 2005.

hi,
I just realized that this must be a difference between sql server 2000 and 2005.
For example, the query is like this:
declare @n int
set @n = -1
select @n = employeeid from employees where companyID=1 and idnumber='1-1'
--select @n
if(@n is null)
......
If there is no such employee, in 20002, @n will be null, but in 2005, @n is -1, not null. Am I right?
So, for this piece, I have to do twice on the same where, like
if(exists(select * from employees where companyID=1 and idnumber='1-1'))
select @n=employeeid from employees where companyID=1 and idnumber='1-1'
else
set @n = null
Any better way?

Thanks.