Okay so the 'little' bug in PPT 2007 is driving you crazy! The fix is on the way with SP2 for Office 2007 (really), but you need to adjust the length of your straight lines today.

Here is a PPT 07 line

To adjust length AND maintain same angle you hold down the SHIFT KEY + CLICK on end of line and it zooms out to infinity

One solution is to duplicate the line, group the 2 lines together, then adjust the length of the group

The original line stays in the same position, the length was adjusted, the angle was maintained! Now ungroup and delete the duplicate line leaving you with the adjusted line (made shorter in this example)

- Troy @ TLC