move mails to folder in a local pst depending on date

dHello
For support reasons we backup mails that are send from the mail server.
Whenever a user complains he didn't receive a mail we can check and prove
otherwise or not . These mails are saved per month, ie. for each month
another pst. Now I have created rules that look when the mail is sent (eg
between 30/6/2008 and 1/08/2008) and the mail is moved to folder 'X' of
backup 200807.pst when the subject of contains 'X'.
Now this system works fine, but a disadvantage is that I need to change this
each month and this takes me too many time and effort.
Perhaps I can use vba to automate this? I am sure vba can help me but I
don't know how... Please advice