Need script to tar files older than 30 days

Hi all. Here's my situation:

I have performance reports that run every 30 minutes saved in the format:

stats_report_11251000.txt
stats_report_11251030.txt
stats_report_11251100.txt
stats_report_11251130.txt

(Obviously run at Nov 25 10 AM, 10:30 AM, 11 AM and so on...)

I would like to write a script that will tar each months report into a tar file named something like stats_reports_November2009.tar

This script will run at midnight on the first day of each month so no special date processing with the file name will need to be done.

How can I do a find on all files older than one month (can't be in days as there are different days in each month) and pipe it to a tar command?

All help is appreciated.

Thanks

#!/bin/ksh 

     set -A mons nothing 12 01 02 03 04 05 06 07 08 09 10 11
     last_year=$(date +"%Y")
     typeset -i month=$( date "+%m")
     last_month=${mons[month]}
     if [[ "$last_month" = "12" ]] ; then
          last_year=$(( $last_year -1 ))
     fi
     touch -t ${last_year}${last_month}010000 dummy
     
     tar -cvf tarball.tar $( find /path/to/logs -name 'stats*.txt' ! -newer dummy)

try that

How do I get tar to remove the files after I've compressed them? Or do I have to do that manually?