Splash screen in WLAN zone for web access

Hi,

I would appreciate it if someone would tell me how they would go about
setting up a splash screen in an 802.11b wireless zone. I have looked
at various proxy server software.

I would ideally like to produce a solution that will run on OS X 10.3.
I do not require any login security facility, but would merely like
to have a splash screen come up the first time users try to access the
web wirelessly from within the zone, before they are passed on to
whatever page they have requested.

Many thanks

James