Here is a reference you can use for building the GUEST VAP. This is only snippets of configuration but it should provide enough info to build the Gust with Captive-Portal.
netdestination ENTERPRISE
network 10.0.0.0 255.0.0.0
network 172.16.0.0 255.240.0.0
network 192.168.0.0 255.255.0.0
!
ip access-list session GUEST_ACL
user any udp 68 deny
any any svc-dhcp permit
any alias ENTERPRISE any deny
any any any permit
!
user-role guest
session-acl GUEST_ACL position 1
!
aaa authentication captive-portal GUEST
default-role guest
server-group internal
redirect-pause 3
welcome-page http://www.arubanetworks.com/
no logout-popup-window
!
user-role PRE_GUEST
session-acl logon-control
session-acl captiveportal
captive-portal GUEST
!
aaa profile GUEST
initial-role PRE_GUEST
!
wlan ssid-profile GUEST
essid GUEST
opmode open
!
wlan virtual-ap GUEST
aaa-profile GUEST
ssid-profile GUEST
vlan 666
forward-mode tunnel
!
-michael