Startup Passwords

Hey guys
Im new to the advanced computer concepts and whatnot, but recently a couple of guys have been messing with my computer, so I want to get a startup password. Not only so they cant mess with my computer, but so they see Im getting smart to it by using a password.

I looked in the power options and couldnt find anything. I also looked for a password icon in the controle pannel but cant seem to find one. In the past I have seen a password icon in there on different computers, but maybe mine is different or maybe these guys deleted the icon so I couldnt do anything with it.

I have windows xp tablet edition, but I dont think the tablet is much different in this department.

Thanks alot
Mike