The version you are using is very old, and no longer available or supported. To extend it beyond 2004, you will need to edit the code, which you are welcome to do.
You'll need to edit calendar_admin.pl, around line #656, you will see the following:
<select name="Year" size=1>
<option value="1997" $yearselected{1997}>1997
<option value="1998" $yearselected{1998}>1998
<option value="1999" $yearselected{1999}>1999
<option value="2000" $yearselected{2000}>2000
<option value="2001" $yearselected{2001}>2001
<option value="2002" $yearselected{2002}>2002
<option value="2003" $yearselected{2003}>2003
</select>
Simply add more lines to add more years.
Unfortunately, due to the volume of email I receive and the fact that this script is old and no longer supported, I cannot offer personal assistance or more detailed instructions on how to make these changes.
I recommend checking out the new version of CalendarScript which has much more functionality than previous versions of the calendar - http://www.calendarscript.com/
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Scott
CalendarScript.com