sql DateTime convert problem

Hi
I'll simplify my problem , i have table with columm  "Issue_dt" smaldatetime
selct * from mytable
the result appear like the following
Issue_dt
-----------
2008-06-15 00:00:00
2008-06-12 13:49:00
2008-06-12 13:49:00
------------
but when i perform the follwong select
Select issue_dt,convert(nvarchar(10) ,issue_dt ,103) ,convert(nvarchar(10),'2009-08-03 00:00:00:000',103) from MyTable
the result comes as following
-------------------
2008-06-15 00:00:00      15/06/2008      2009-08-03
2008-06-12 13:49:00      12/06/2008      2009-08-03
2008-06-12 13:49:00      12/06/2008      2009-08-03
2008-06-12 13:49:00      12/06/2008      2009-08-03
---------------
my question is why the sql server convert the constant value  '2009-08-03 00:00:00:000'  to  2009-08-03 NOT to 03/08/2008 despite i use the same format in convert function ?
This cause a big problem in my VB.net application  because i sent a parameter to SP  with values like ''2009-08-03 00:00:00:000' to use it in Where condition to compare between the date only that stored in issue_dt column so when i use
convert(nvarchar(10),'2009-08-03 00:00:00:000',103)  it consider it as  2009-08-03 not as 03/08/2008 ? so how can i solve this problem