First of all, i'm not sure if what you want to do is possible as it would make it possible for an unauthorised user to access your user. Secondly, however, i can think of 2 ways to do something similar.
1) remove your password - you dont want it you can get rid of it by clicking on the start orb and clicking on your user picture, from there select remove password.
2) don't turn off the computer, instead you can put it into hibernate, this way (if my memory doesn't decieve me) it will not prompt for a password.
i.e. bypass that screen
I'm using Vista Home.