When I need something like this, I create an appt with a reminder - in your
case, a 30 day reminder - and never dismiss it until its done. Another
option is to set it for a recurring event and edit it when you are done to
end the recurrence. You could use tasks instead - it really depends on your
needs and habits.

I used to use tasks then upgraded to Outlook 2007 and prefer to make
appointments (usually for after 3 pm) so I can see them on the to-do bar.  I
have too many flagged items on the task list and often have too many
reminders popping up, but upcoming appointments are big and bold. :)