That's the thing, the DHCP server is an add-on package in DSM4 but now it is built in DSM5.
In DSM5, the options DHCP Server, DHCP Clients and DHCP Reservation
can be found in : Network > Network Interface > LAN1 > Edit
I could install an ESXi and give it a shot with a brand new install, but I thought asking for help in the forum first.
Anyone using DHCP server in "DSM5 4458 update 2"can advise ?