We did this in SAS 9.1 by:
- Editing the public portal page, via sasguest (who owns it by default)
- Adding a text portlet with the disclamer text
- Adding a text portlet, that contained the login form (scrapped from the login page html)
- Directing all users to the public page not the login page
We also added a url portlet that showed the EDW load status
You will need to renable the public home page (its off by default in 9.2) but it should work.