I would go into:

Control Panel -> Mail, or Control Panel -> User Accounts -> Mail, depending on the view of your Control Panel. click on "profiles" and find the outlook profile you are using and check the path of the actual *.pst file that Outlook is working off of. Since Outlook is working there has to be a *.pst file somewhere, it is just a matter of where and what name it is using.

When I get home I can get into more specific details on the defaults of where Outlook creates the *.pst files if you need them. (it is Friday however , it might be late)

Edit: When you are in Outlook '07, just go to Tools -> Accounts -> Data Files, Tab and it should list the *.pst files associated with your account.