The "trick" with Xming is to FIRST start it via the XLaunch (icon or command), NOT the Xming command/icon. That's because XLaunch allows you to check "No Access Control" which tells Xming to allow other IP's in. Starting Xming with the Xming command, causes the default "only allow in local host" mode.
I was confused by this and first started Xming via "Xming" and didn't understand the role of XLaunch.