You can do this by scheduling your backup job. Keep in mind that in
order to set this up you'll need a user account that has a non-blank
password.
If you have Windows Backup still configured to start in the default
Wizard mode, click on Advanced Mode in the opening screen.
You should now see the Backup Utility. Click on the Jobs tab.
At the bottom of the calendar, hit the Add job button.
In the Backup Wizard, hit the Next button.
On the What to Back Up screen, select Back up selected files,
drives, or network data. Hit the Next button.
On the next screen, select the folders and files you want to back
up.
On the next screen, select the location you want to store the backup
file and assign a name to your backup job. Keep in mind that you
will not be able to select your CD or DVD writer as a location to
store the backup unless you have packet writing software, such as
Nero's InCD, Roxio's Direct CD, or Sonic DLA, installed on your
computer.
On the next three screens, select the appropriate options for your
backup job.
On the When to backup screen, select Later, enter the job name, and
hit the Set Schedule button.
If you want to run this backup job manually, select Once. If you
want the backup job to run automatically, configure the schedule
however you want.
Once you've set your schedule, hit the Next button.
Enter the password for your user account twice and hit the OK
button.
Hit Finish.
To run this job manually, go to Control Panel -> Scheduled Tasks and
right click on the icon representing your backup job. Select Run
from the menu.
If you configured this job to run on a set schedule, right click on
the job and select Properties from the menu. Click on the Settings
tab. Put a check mark in the box next to Wake computer to run this
task. Keep in mind that your backup job will not run if the computer
is off.
For more info, click on Help in Windows Backup. Select Help Topics
from the menu. On the Index page, scroll down to Scheduling tasks.
Click on backup jobs and hit the Display button. You can also take a
look at this article.
Windows XP Backup Made Easy
http://www.microsoft.com/windowsxp/using/setup/learnmore/bott_03july14.mspx
Good luck
Nepatsfan