Move Shape Across Screen

I'm trying to write some VB to draw a line shape and then move it across the screen. I have managed to draw the line and have used the following code to move it:

Set linetest = ActiveSheet.Shapes(1)
For iCount=1 To 100
linetest.Left = linetest.Left + 1
linetest.Top = linetest.Top + 1
Next

i) I can only actually see the line move if I run the code using the debugger and step through the loop. If I just run the code then I only see the end position of the line (note, this is not an issue with the calculation being too fast for Excel to display the line. I tried the code with a delay loop in it and it made no difference). I can get it to work by calculating the active sheet for each iteration of the loop, but this means I have no control over the speed of the movement; incidentally it moves very slowly).

ii) This seems a poor way to move the line. Is there anyway to move the start and end node of the line rather than using the left, top, width and height properties (i.e. can I get the old coordinates of the points and set them to different numbers)?