Reidar,
In my opinion is it than better to use a more selected approach, your user
will love you.
Give him first a combobox with years and than beside that with a month (the
calender is another approach however than he/she will probably not love you)
and than make a selection with a "where" clause depending from the text from
the combobox that he/she selected. To avoid typing errors you can use the
dropdownstyle. The month you can give in names while than the selectedindex
is your month. The year is in numbers so that is easy
And than use a button to start, so that when he does not select something
gets it all. (And than it is his/here choise to let it be a long time)
I hope this helps,
Cor