Hi Sn1p3r,
First off create yourself a new VLAN ID (let's say 10) on both switches.
2. Switch Configuration
8. VLAN Menu
2. VLAN Names
Once that is created add the ports 5-10 on both switches as "untagged" to VLAN 10.
2. Switch Configuration
8. VLAN Menu
3. VLAN Assignment
On the ports which connects both of your switches together under VLAN 10 set it to "tagged".
This will isolate ports 5-10 on both switches from the rest of the ports but will allow them to communicate between the two switches.
As long as your DHCP server is connected to one of the ports that is a member of VLAN 10 then only devies connected to VLAN 10 ports will be assigned a dynamic IP address.
Hope this helps.