With xp the only way that I'm aware of you will have to have two boot options 1 being the normal winxp the other being the edited version (I guess it has something to do with windows fixing itself everytime you shut down) and the other being the edited winxp.
Google "log in boot randomizer" er "loginbootrandomizer" or something to that effect. I'm pretty sure that you will come up with more detailed instructions.

I was considering this, but decided against it due to the fact that when I push the button on my computer I want it to start up as fast as posible and not have to go through any type of options.