Say i have two hard disks

Disk - A
Disk - B

Now lets assume my friend is working on the linux red hat 2.6 with Disk A mounted with lot of our project files.

Disk -B is of mine , say i wanted to copy some data from Disk-A to Disk-B,
the usally procedure is to mount the Disk -B and use it in my system.

Here are my queries.
1. Say i wanted to secure my friend hard disk with a simple password, what is the

I am planning to write simple shell script , should i put that in /rc.d that is at boot time, (if the DISK -A is non bootable && bootable scenario) in DISK -A ? .
So that say if i try to mount DISK -A then try to copy the contents into DISK -B It should prompt for enter password else should not provide access to DISK -A.
I know it is not strong method of protecting, but atleast to start with.

2. If the Disk -B is also bootable disk, then on mounting what will happen?