Q I sometimes have to reformat my hard drive to get Windows working properly. But when I do this, I lose all the names and fax numbers I've entered into Microsoft Exchange, plus all the e-mail addresses I've stored in Internet Explorer's e-mail program. Can you please tell me what files to back up?

A Microsoft has a habit of hiding data. Depending on the version of these programs you're using, the versions you've used in the past, whether you share your computer, and, quite possibly, how often you brush your teeth, your address book files can end up in all sorts of locations and with all sorts of names. One constant: they don't end up in C:\My Documents, where they logically belong.

Another constant, thankfully, is the extension. Both Microsoft Exchange and Windows Messaging address books, which can contain e-mail addresses and fax numbers, are always .pab files. In Internet Mail and Outlook Express, however, they are .wab files. (Microsoft Exchange and Windows Messaging are different versions of the e-mail/fax program that comes with Windows 95; Internet Mail and Outlook Express are different versions of the e-mail program that comes with Internet Explorer and Windows 98.)

Before you format your drive, find your .pab or .wab file: select StartûFindûFiles or Folders, in the Named field, enter either *.pab or *.wab, depending on the program you're using, and hit <Enter>. If the search yields only one file, that's the one to back up. If there are multiple files, the right one is likely to be the one with your name (kent.wab, for example), or the latest one. To be sure, enter the mail program, add a name to the address book, exit the program, and go back to the Find program and click Find Now. The right file will be the one with the most recent time.

Restoring the file on your new PC is trickier, because the new installation may look for a file with a different name and path. For instance, on the old setup, the file may be in C:\Windows\Application Data\Microsoft\Address Book\UserMPS.wab; and on the new one in C:\Windows\Profiles\Kent\Application Data\Microsoft\Address Book\kent.wab.

As described above, search for the name and location of the file in the new setup. Once you've found the file, note its name, and then rename it to something like holdit.wab. Next, copy the old file to the same folder as the new one. If necessary, change its name to whatever the new file was before you renamed it.