guest network using tagged VLANs

[Simon Hobson]

To expand on Rudy's reply ...
As said, configure the AP to connect one SSID to one VLAN, and another SSID to another VLAN - this is then functionally equivalent to having two APs on separate physical LANs.
At the DHCP server, have the daemon listen on the two VLAN interfaces and define subnets to match. Again, this is functionally the same as having two interfaces connected to two seoarate LANs.
The rest just happens automagically - no special rules in your DHCP config.
This is something I've done a few times both internally and for clients.

Simon