After populating the drop-down as I mentioned in step 1 of your question, you can use the User value to populate a task assignment. In the dialog workflow component, the "person assignments" on the Assignments tab can be used to assign a task to the user. Use the PrimaryEmail column for this value. If you're trying to add a task assignment after the fact, you can use an "Add Task Assignment" component and select "dynamic value". Map in the ReferenceID (UserID), ReferenceName (PrimaryEmail), ReferenceType (right-click and select Create Constant, then double-click the mapping arrow and select User), and TaskID (this will be the task ID to which you are adding an assignment - if you're adding this inside a Dialog Workflow component, it will be the workflowTaskId variable). Again, send me a PM if you want me to assist with a quick webex.
EDIT: I should point out as well that the assignment doesn't actually happen to a queue, it happens to groups in that queue. So when an assignment targets a "queue", the queue is fetched, the member groups of that queue is fetched, and each group is targeted then for assignment. The "queue" is essentially just a container for those groups. The queue name, ID, and type does save to columns in the IMIncidentTicket table though for reference.
-africo