Make sure the management VLAN and the two VLANs you are trying to access are both trunked to the AP. Create two VLANs on the AP with two different SSIDs and security settings. Make sure there is a DHCP server on each access VLAN.
If you have users from both VLANs getting IP addresses from the same firewall before installing the AP, it will work the same way after installing the AP. First make sure the wired VLANs are setup correctly, then add an AP to a VLAN trunk to allow wireless users to access those VLANs.