I have windows vista, There are two administrator rights on the system , one of them is i , I want that second administrator should not able to see my data , what i have to do for it please help me.

Is this a personal computer or work computer? If this is a work computer if advise that you don't do anything unless you are sure that it won't violate anykind of computer usage policies.

If this is a personal computer there are several things that you might be able to do. If you're computer is formated with the NTFS filesystem you can use windows file encryption system. This article is for XP but it is similar for Vista. You can also use third party encryption software. Something else you can do is to change the other user's account type if the other user doesn't need to be an administrator. You can do so in the User Account settings page in control manager. There is a tutorial on user accounts here. You will also need to make sure that you are the only one that can acces your documents folder & a tutorial to do so is here. Of course you'll also need a password if you don't already have one.