Yeah. When you start the computer it'll probably ask which one you want to use. If it doesn't, it'll just start the other one.
Yes. There is a process called Dual Booting, but it requires two hard drives. Just search for "how to dual boot windows vista and windows XP?".
Windows Vista does not officially support booting from a FAT32 drive, although it is technically possible. Vista supports FAT32 on Flash drives and hard drives, although it will not format a hard drive over 32 GB as FAT32.
Yes. Any hard drive, flash drive, or other external storage device that conforms to the USB Mass Storage device standard will work on Windows Vista.
The hard drive stores the Operating System. Like for example : Windows XP or Windows Vista or even Windows 7 without the hard drive your computer will not turn on.
Install Win XP on the first hard drive, then install Vista from Xp and on question about "what kind of installation do you want to have?" Answer "separate" installation. When it asks you "which hard drive are you going to use?" Choose the second one. Vista will create a boot list automatically.
Bit locker
Windows Vista laptops will only be available on the second hand market. In addition, it will be difficult to obtain drivers for a modern laptop that officially support Windows Vista. It is even hard to find a Windows 7 powered computer, as Microsoft is pushing Windows 8 hard, despite its unpopularity.
Yes it can, but you will have find drives.
Hard drives for windows and OSX vary in size and model, check or ask about your computer brand. You can also check in My Computer (for Windows) or Macintosh Disk (for Mac OSX).
You can not simply downgrade to Windows XP from Windows Vista. If you want to completely remove Windows Vista in favor of XP, you will have to format the hard drive and reinstall the OS from scratch. Windows XP will not install on top of an existing Vista installation.
Windows XP does not "have" a hard drive. The hard drive is a part of the computer, not Windows XP. Windows XP supports only IDE drives natively, although OEMs can also include drivers to support SATA drives.
Yes, you can. If your computer has more sata ports you can use then to connect more hard drives.