say the VLANs are vlan 10 and 20.
on the core switch --> assign IP address to VLAN 10 and VLAN 20.
enable "IP forwarding" in the switch.
on the DHCP server, define scope for VLAN 10 and 20 and set the "default router" to the IP address you configured on the core switch.
configure "ip helper address" in the switch's VLAN interface, if the DHCP server is residing in a differnet VLAN.
you are done.