Also if your company needs a SOX compliant banner and you want it to look purdy:

I originally used the solution
http://www.afp548.com/article.php?story=lion-policy-banner
and made it look okay with an image, but then I tried to log on with a user from our AD domained/bound accounts.

We have a .local domain which causes crazy long login times, up to 3 minutes (see my other post we, also have a call in with apple)
because the Policy Banner is set to re-appear after 30 seconds of inactivity it would nullify the attempted login for AD users


So I found another way
Replace:
/System/Library/PrivateFrameworks/LoginUIKit.framework/Versions/A/Frameworks/LoginUICore.framework/Versions/A/Resources/appleLinen.original.png

with a large resolution file (we use 1024x768) that has a transparent background (has to be png)
I put my text as well as the apple log in the middle and fiddled with the location of both of them until it looks nice above the username/password fields


Thanks!