Use
DateTime[
^] to get the years, do string concatenation(Ex. 2010-2011) & add it to dropdownlist.
DateTime.Now.Year()
will return current year.
EDIT
Agree with Prasad. Store values in database & load it in dropdownlist. Consider this is your table(Academic_Years).
Years
--------------
2008-2009
2009-2010
2010-2011
2011-2012
--------------
Use below query to select the data
SELECT * FROM Academic_Years
Write code something like below
DataTable dt = GetYears();
dropdownlist.DataSource = dt;
dropdownlist.DataBind();
Finally I suggest you to learn everything
ASP.NET Tutorial @ W3Schools[
^]