The Vista tool used to encrypt an entire hard drive is BitLocker Encryption.
Bit locker
Kakasoft Advanced Folder Encryption has a function that helps you to hide a entire hard drive. If you need it, you can visit their site: http://www.kakasoft.com/folder-encryption/how-to-encrypt-files.html
There are many types of software that can be used to encrypt a hard drive. One would be likely to use a program such as GNU Privacy Guard since it is a popular software.
Since you are using Win 7, you can encrypt entire hard drive with BitLocker. Search "BitLocker" on google, you can get many how-tos about encrypting drive. If you don't want to encrypt the drive or you are afraid you will lose all content in drive when forgetting the password, you can also use third party software such as Kakasoft Advanced Folder Encryption to lock and hide drive with password.
In general, TrueCrypt is considered to be one of the best encryption tools around. You can even encrypt a separate partition on your hard drive.
There is no "DOS mode" for a hard drive, and it is not necessary to use DOS to format a hard drive. Vista's installer had a built-in partitioner and formatter.
NTFS (New Technology File System) file system is the only file system that is able to be encrypted fully
You would either encrypt the data, or and, encrypt the folder or hard drive, flash drive, etc.
No. Vista ruins all windows(non-vista) and RAIDed partitions.
BitLocker Drive Encryption
The main drive is the drive with your operating system on it.
insert the windows vista disc. It will give you an option to upgrade or do a clean install. Choose clean install. It wipes your entire hard drive and installs your new vista, just as you would buy it brand new in a shop! i do this every 6 months, its the only GUARANTEED way, to remove any virus.