There are technically 3 Org Network types (really 2, and one that's a variation on the two).
1. Direct External Org Network
If you put a VM onto this, it goes directly onto the External network. It takes an IP from the external pool, and just runs with it.
2. Isolated Org Network
You basically "make up" a network. This will not have external access ... if you attach a VM to this network, it can communicate with any other VM on this exact network.
3. Routed Org Network
it's like #2, but with a vShield Gateway that would be created. This vShield edge would perform the functions of your "default gateway". Think of this as a large private network, or a massive N:1 NAT.
If you just want to give a bunch of people internet access, you can put VMs on here and make a Firewall rule to allow all outbound traffic and put it through a single IP (which would come from your external network).
RE: 1 - this is a value inside the network you are defining. let's say we want our gateway to be 10.150.10.1 on a /23 ... when you create the network the gateway will have an internal IP of 10-.150.10.1
RE: 2 - this is just a range to assign out to VMs put onto the network. say 10.150.10.100 - 10.150.254. These will become IPs which vCloud will delegate to a VM's NIC card as they are created.
