It allows you to reference an external server. Here is the config guide, check pages starting on page 55:
This shows the config and how / where to enable this feature.
I am also interested in setting up this feature. Does it assume you have web pages already setup to handle a logon request from the wireless client, handle valid/invalid security details and then allow access to the public Internet when authenticated? Are there no samples available that can be used to get things up and running much quicker? If you have any further details on this it would be most appreciated.
The http redirect will send the first time http request to a page off of a server that you have set up and or defined.
I do not have any examples of company websites that list an acceptable use policy. You might try to google something to see what other companies have set up as an acceptable use policy.