I have done this before, but it is a little involved.
First you should make sure that Power Archive has command line capability.
If that's good, then here is code that I used with pkzip some time ago:
@cls
REM @echo off
REM
REM Batch File Name:
REM SCHED_BACK.BAT
REM
REM Description:
REM Compress files and subdirectories on Development
REM into a file to be backed up.
REM
REM Functions:
REM 1) Calls Sched_back_date to set Sched_back_DATE variable
REM 2) Backup files using PKZIP
REM
REM Parameters:
REM 1) Day of Week (Abbreviated - Mon, Tue, etc)
REM
REM
REM Modifications:
REM 16-Oct-1998 R. Willard initial version
REM 13-Aug-1999 R. Willard Added backup for Web directories
REM Backup file now contains day of week
REM
REM ========================================
...
CALL Sched_back_date
SET Sched_back_FILE=backup_%Sched_back_DATE%.zip
\Pkzip\pkzip25 -Add -Dir=specify %Sched_back_FILE% "\folders\files.txt"
This is how I set the date, you will want to make sure you have QBASIC to do this.
REM Batch File Name:
REM SCHED_BACK_DATE.BAT
REM
REM Description:
REM Sets sched_back_DATE environment variable for use in
REM Sched_back for naming the backup file.
REM
REM Functions:
REM 1) Writes basic commands to $sbd$.bas
REM 2) Run $sbd$.bas using Qbasic
REM 3) Builds $sbd$.bat which is called to set variable
REM
REM Parameters:
REM 1)
REM
REM Modifications:
REM 4-Nov-1998 R. Willard initial version
REM
========================================
REM
echo>$sbd$.bas open "$sbd$.bat" for output as #1
echo>>$sbd$.bas ? #1, "set Sched_back_DATE=";DATE$
echo>>$sbd$.bas done:close #1:system
qbasic /run $sbd$.bas
call $sbd$.bat
del $sbd$.ba?
Hope that is of some use. Can't believe I found this code on one of my many backup CDs.