There is as yet no GUI for the Multi SSID. You can read about the development of this on the linksysinfo.org forum: http://www.linksysinfo.org/index.php?threads/vlan-tags-work-for-you.34478/page-5
Re. the missing DHCP - not sure what you mean. DHCP is in the BASIC/NETWORK/LAN page. But I'm sure you know that, so I guess something is wrong. However, when 2405 was built several months ago, many people used it and none reported missing DHCP. If it didn't have DHCP it would have been useless to anybody.
But there are much newer builds, the one you have is quite old.
EDIT - I have your PM now and understand that you have now found the DHCP. That's a relief!