I've accidently done it a couple times but can't figure out what combination of buttons I need to press to make the view rotate instead move around when I press the middle mouse/scroll wheel.

Does anyone know this?

Thanks

You need to middle-click the Bottom Half of the Screen, I discovered this when I was playing Populous: The Beginning, you can also rotate the Screen using the DEL (Delete) and PGDN (Page Down) Keys and you can set the arrow keys to move sideways and Hold Down CTRL to Rotate the View.