If you want to create a Public Folder in Exchange 2003 you have to:
Open the Exchange System Manager and go to:
Administrative groups -> ‘Administrative group’ -> Folders -> Public folders.
Right click on ‘Public Folders’ and select New -> Public Folder.
Now give the public folder a name.
When done you can press Apply or Ok.
If you want to public folder being able to receive mail, you can right click on the just created Public Folder and choose Tasks -> Mail enable.
In the properties of the public folder you can assign an email address to the public folder.