I used the windows xp backup program to backup our computer. I thought that it would make a copy of the outlook express address book but when I tried to find it in the "restore" section (c:\documents and settings\"user"\application data\address book) the folder (\address book) was empty.
Is the backup program unable to copy these files - or are they not visible from the restore program?
The address book file is technically hidden, but the backup program shouldn't have a problem finding hidden files. If you want to try to do a manual backup you can search for the address book on your own(assuming you still have the original files as I'm not sure what you have done up to this point)
C:\Documents and Settings\
Right Click on your user profile -> Search
Under More Search Options make sure Search Hidden Files and Folders is checked as well as Search Sub-folders
In the search bar type "*.wab" without the quotes.
This will search for any Windows Address Book(.wab) files. If you find them then just copy them manually to whichever location you want.