the "task board" comes up in the dashboard showing the tasks from an iteration that is not what I want to see.
How make the task board come up with the iteration of my choice (without having to select it every time)
If memory serves me the Task Board should default to the iteration currently in progress for the current date in the project to which you're scoped. This is not configurable.
Hope that helps.
But I have 2 simultaneous iterations in that project... and Rally is auto-selecting the one I don't want...
I think that the one with the earliest end date will be auto-selected, or the one that you created first if they have the same dates but in any case the answer is that you can't change the configuration to select a specific iteration first.
I'm curious about the simultaneous Iteration Timeboxes for the same project. What is the problem/issue that is solving? Just curious.