[Andy]

Select a single object, then use Tools > Object Properties Editor to set the loc x, y and z values. That will move the object center to the location you specify. If you are not seeing a window popup then it may be off-screen and you might need to reset your preferences.

The rotate mode allows you to rotate around the object center (the object's "loc") using the mouse. It will rotate around the axis you are looking down from e.g. rotating in the X, Y window, rotates around the Z axis. These rotations are 'axis-aligned'.

If you want to rotate around a different axis, you can make a single line object (i.e. a two vertex line), or select any two vertices. The line between the two vertices is be used to specify the axis of rotation when using the "C" rotation (press C on the Rotate section in the control panel, and then press "set axis" (making sure the line you made is selected). The info at the bottom of the window will let you know that AC3D got the vertices ok. Then set the angle you want your object to rotate around this axis and, making sure the stuff you want to rotate, not the line, is selected) press rotate.

This looks more complicated written down than it is to do. Let me know how you get on.