How to Backup your PST Files in Outlook
1. Go to your Outlook folder in Windows Explorer
NOTE: To find your data file select File | Data File Management. Select your main data file (named Personal Folders by default). Click Open Folder.
2. Select all .pst files
WARNING: Ensure you select both "outlook.pst" and "archive.pst".
3. Copy both files.
4. Paste both files in the desired backup folder.
Tipit's best to store your backup on an external storage device. You will either need to manually make regular backups or, do what I do, and use a backup program to make sure you always have the latest data backed up.
To restore your pst simply close Outlook, copy the backup pst to the default Outlook destination and your Personal Folders will be fully restored. This comes in very handy if you have had to re-install Windows and need to set up Outlook again