You can create a sub site for
various categories. For example:
- Departments
- Products
- Projects
- Team
- Clients
- Suppliers
- Customers
- etc.
The URLs for each will be,
for example:
http://yoursitename.wss.episharepoint.com/finance
http://yoursitename.wss.episharepoint.com/marketing
You can manage for sub site
separately so that access is
restricted while maintaining
global access to the parent
site.