Tablet's users will be able to use different profiles since JB 4.2, defined at system settings level (settings -> user profiles). How can I set a password for each profile?
Each user account has its own lockscreen settings, so the easiest way to do this is to simply use a password lockscreen for each user. In fact, you can use entirely different lockscreen security for one user than you do for another (e.g. one could use a pattern, one a PIN, one a slide lock, etc).
To set this up, select a user and unlock the device, then go into Settings => Security =>Screen Lock and select the "Password" option (you could also use PIN or pattern, of course). Set the desired password, then lock the device. Repeat this process for each of the other user accounts to set up individualized passwords for each one.