The previous responses to your question basically sum it up. You can,
however, type in the co-ordinates of either end of your line, or the
centre of the line using the transformation docker window (select
position option). Firstly, draw the line. Then, you choose the end of
the line you want to give a co-ordinate to (by selecting the
registration point in the docker window) and then type in the values.
0,0 is the bottom left hand corner of the page. The line will shift to
the point you entered.