nick59007,
The problem you are running into can simply be handled with Vlans (virtual local area networks). The RV325 comes out of the box with vlan 1 (private), vlan 25 (public), vlan 100 (phones). The issue you explain could be solved by placing your private (staff) network on the vlan 1 and public network on vlan 25 (access this by setting up the port managment - port membership).
You will want to make sure that the DHCP is setup to 2 different networks (for example 10.0.1.0/24 and 10.0.25.0/24).
I think you are probably just wanting wireless clients to access the vlan 25 so you will set that up in the WAP under your radio networks (there is a vlan id field). if you want staff to use wireless as well you can set that up too just add a second AP and assign it to the Vlan 1.
NOTE: WAP321 supports the captive portal which essentially allows you to have your public users accept a usage policy so you're not viable for the data consumed by the public users.
-Jason