Turning a monitor around 90 degrees

[stigmata]

Hi

I want two 2001fps standing next to each other in "portrait" (i.e. turned round 90 degrees), but with a third small monitor standing normally. However, I cant find a windows software setting that makes this work (e.g. when I move the mouse on to the dell monitor, suddenly up-down becomes left-right). Am I missing something obvious or do I need an application for this?

Thanks