trustnot maybe you werent paying attention. Dr Evil answered your question. No you can not stop your grandfather from changing the boot sequence without a bios protection password. you dont want to do this so you answered your own question. Now I am guessing your grandfather and you use two different login names and passwords. now if you set it up so that you both use different credentials then you can setup securtiy.


Log on using your administrator account
right click on your folders
Go to properties
Click on security tab
Click add,
Click and choose your username
Then
Remove Everyone, (except your own account)
Now when your grandfather logs on using his account, he will be able access your folders.
What this does is remove permissions from anyone being able to access the account. NO MATTER WHO LOGS IN. I am not yelling there just making the point that it doesnt matter what hard drive you boot off of this is what will happen
your grandfathers drive is booted master yours slave.

-->No one can access your hard drive without your login credentials and password.
scenario 2 your grand father boots master off your hard drive
--> he cant even login because he doesnt have credentials to your hard drive

scenario 3
--> lets say you give him credentials to run your hard drive BUT you dont put his login name into the security tab of the folders you want him locked out of, he cannot access these folders. unless you give him admin privelleges and he takes control which takes more of an advanced user to figure out how to do this.

Now I think that is answering what you were wondering??