use IIS to add a footer to everypage it serves. Or maybe you can use shared
border and put your disclaimer  in it.

I tried just that (since I too needed to put a disclaimer  on every page
on my SPPS 2003 site  and sub sites). However it does not work. I most
likely am not doing all the steps.

This is what I did:
Created a disclaimer.html file on the share point  server's root disk
(path c:\disclaimer.html)
Launched IIS Manager
Under Web Sites, selected ProdSite
Right Clicked -> Properties
Selected Documents Tab
Checked "Enable document footer"
Clicked browse and browsed to c:\disclaimer.html
Clicked OK
Closed IIS
Did IISReset
Launched SPPS 2003 web site -> Logged in and it started giving me all
kinds of errors on "browseris", prompting me to debug <Yes> <No>, I kept
on clicking NO and finally when the site was displayed I did not see the
footer.

I removed the footer (disclaimer.html from IIS -> IISReset -> Launched
site... works fine without the footer.

This will not work, Sharepoint implement a ISAPI filter which take over page  rendering. The only easy way I can think ok is to change either
change every default.aspx page or
change the Page template to enable a web part with your disclaimer

In any case, there is no easy way

how about thru one of the site  definition files? \template\1033\xml\ ont.xml which allows you to change the items in th menu bar etc..I need to investigate this more. The only other way is to modify the tempates such as STS#0 etc