I have setup a WAP with 2 SSIDs, one untagged and the other on VLAN tag 8. I tested it with one 2960 switch and I can get to my corp lan on the untagged and can get to a public TimeWarner connection on Vlan 8 SSID.
Once I have added a couple more switches to the mix I cannot get the VLAN 8 to give me an address for the public connection. On VLAN 8 SSID, I get an address from my corp DHCP server but should not.
I think the tags are working because when I connect to the VLAN 8 SSID and get a corp address, I cannot get to the Internet.
When I connect to the SSID for the corp lan, I get a corp address and can get to the Internet.
I have attached my setup that work and don't work. No routing between VLANs is needed.