Move a point (vector) on the same path

[Stephan Dube]

Hello
I had a quick question
In Illustrator CS 4 is there a way I could move an achor point (vector) from a path but it follows the path?
For example if I create a 45degrees line and I want to take the furthest point and move it to the same angle (45 degrees) but make the line shorter how would I do this?
thanks
cheers
stephan