Setting up "open" wireless access point

I need some suggestions on this one...
The purpose is to create an "open" hotspot that would allow the access to network resources upon entering a user/pass on a portal. No other resources except the portal should be accessible without a login (this has to be set in a room where guests come, some of them should be able to use the connection, some not...)
Requirement: all software must run on Windows and must be freeware.
Ideal outcome: based on the account used for login, access will be given to internet only (no LAN) or both to internet and LAN.
Acceptable outcome: only internet access will be granted for all users (they would later use VPN to access local resources).

I was looking into the chillispot solution, but it seems it has support for *nix platforms only. Oh, I should mention that the wireless AP is a Linksys WRT54G router, so custom firmware can be installed. A RADIUS server is available (IAS in Win2K)
Suggestions???