They should be in one of these locations, the GUID is a string of numbers :
C:\Windows\Application Data\Outlook Express\{GUID}
or
C:\Documents and Settings\<User>\Local Settings\Application Data\Identities\{GUID}\Microsoft\Outlook Express
You may need to show hidden files :
1. Click Start, and then click Control Panel.
2.Click Appearance and Themes, and then click Folder Options.
3. On the View tab, under Hidden files and folders, click Show hidden files and folders.