Disable MS Office Open File Address Bar

WINDOWS 98 SE:
Is there any way (through registry edits or other means) that you can disable a users ability to type in an address in the MS Office Open File window?

We have it so that the system folders are hidden, and the address bar in Windows Explorer denies users the right to type anything in. That way they cannot access the folders. However, if you go to open an Office document, you can type in the address (such as c:\windows) and go to that directory. I want to disable this ability. Any ideas?