How do I get a single VLAN to work between 2 HP switches?

Here in a large college we need to have our wireless access points on one VLAN so any DHCP requests from wireless devices can be assigned a different subnet, instead of picking up IPs for the usual wired network.

As a test setup I have been using a HP Procurve 4108GL switch and a smaller ProCurve 6108. The test wireless AP connects to the 4108, as does my machine. The DHCP server is on the same subnet as the Wireless APs and is connected to the 6108 switch.

I have got the VLAN working correctly on the 4108GL between myself and the AP, however I cannot see the DHCP server at all from my machine... I think my setup of the 6108 is missing something fundamental.

Access Point IP = 10.3.56.11
DHCP Server = 10.3.56.101

4108GL settings:-
VLAN ID = 3 - (ports for AP and my machine are untagged)
VLAN IP = 10.3.56.1/23 (range = 10.3.56.0 - 10.3.57.255)
VLAN 3 IP on 4108GL = 10.3.56.254
IP helper-address = 10.3.56.101

6108 settings:-
VLAN ID = 3 - (port for DHCP server is untagged)
VLAN IP = 10.3.56.1/23
VLAN 3 IP on 6108 = 10.3.56.253
IP helper-address = 10.3.56.101

As you can see, I have not untagged the port on the 4108 that the 6108 connects to as other servers are in the mix and I didnt want to ruin the network. This VLAN is only supposed to see itself, which is does except for not seeing the DHCP server, which is kind of crucial.

So Im stuck - is there a better way of doing this? Maybe having the DHCP on different VLAN ID? Or does it come down to me not untagging the port on the 4108 that talks to the server?

Thanks
Pete