Introduction to VLANs

So if I have a 48 port switch on the 198.168.1.0/24 network…… and all 48 ports are connected to host. All the host have IP addresses on the 198.168.1.0/24 network. And lets say I create 4 VLANs. Help Desk is on VLAN 10 (interface 1-12), MGMT is on VLAN 20 (int 13-24), Accounting is on VLAN 30 (int 25-36), and Supply is on VLAN 40 (int-37-48). OK…. So these 4 VLANs would basically share the same network (198.168.1.0/24) right? VLANS don’t have to be on different networks/subnets?
What if there were some other MGMT host on another router on a 10.10.10.0/24 network…. Could those join the above VLAN 20 as well?