Difference between 'Custom' and 'LAN Segments' networking options in VMWare 8?
VMware uses the concept of virtual networks, often identified on the host as vmnet0-vmnet9 (there can be different numbers of vmnets depeding on which version and exact VMware product you are using). By default Workstation sets up vmnet0 as a bridged network, vmnet1 as host-only and vmnet8 as NAT. When you select "bridged", "host-only", or "NAT" for a given virtual adapter, VMware is really selecting vmnet0, vmnet1, or vmnet8 for you behind the scenes.
A user can configure other vmnets, with whatever properties he wants. Let's say you create a vmnet2 with host-only properties. When you select the "Custom" network type, you get a dropdown that lets you pick the exact vmnet you want. You could select vmnet2, or you could select vmnet0 and get the default bridged network behavior.
"LAN Segments" are a hold over from the Teams feature that was in WS 5 - WS 7.x. LAN Segments function a lot like a new host-only vmnet, but without a DHCP server configured. The idea is to give an upgrade path for Teams created in a previous version of the product.
You could simulate the effect of a LAN Segment with your own custom vmnet if you wanted to, but users familiar with the old Teams might like to use the LAN Segment setting.