OK, so I think I understand where I was going wrong.
When I type .x (etc) I need to me in the midst of the command that is "requesting" me to select a point. For example, if I type .x before I start the circle command, it will default to explode. If I start the circle command and it asks for the centre location, using the .x should properly allow me to select my centre based on an existing x co-ordinate.
Thanks for your help. You can be sure that I'll post again if I have any continued problems.
Sarah-Jane
aka "the newbie"