[Hampshire] Wireless gateway software

Hi,

We're going to trial some "public" wireless access points here at work.
What I'd like to do is provide a similar service to public hotspots like
those in coffee shops where any attempt to view a web page is redirected to
an authentication web page. This should authenticate the sumbitted username
and password against our LDAP server. Access is then allowed to web pages.

Our firewall can handle the outgoing traffic restrictions, but the key
thing is that all the relevant client settings should be dished out via
DHCP. These aren't systems over which we have any control.

So, has anyone used a wireless access point, linux distro or software to
provide this sort of service? If so, any recommendations or warnings?

Thanks,

Tony