The OS is XP. The window that pops ups is a text window that allows you to type some info to the host. This then kicks on the DUN client, the text window goes away and you should be off to the races.
When you're in the DUN client, under the general tab, click "Configure". This will bring up the modem properties. Then check the box that says "Show terminal window". Working with Mitel engineers, this is what they had me do. I thought I could script the text that needs to be entered once I actually got it working manually but I can never get that far.
Ralph