Yes Partition Your Hard drive into 2 "partitions" and it will Dual Boot. See: http://www.pcworld.com/article/73826/stepbystep_partition_your_hard_drive.html
No. Vista ruins all windows(non-vista) and RAIDed partitions.
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.
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.
If it has the minimum RAM and hard drive space, you can.
Yeah if there professional's.
Yes. The SATA internal hard drive in Vista can be turned off, by turning off the feature in system BIOS.
Yes, if it's formatted to FAT or NTFS.
at least 15 gb
No, you only need a bootable DVD drive and enough hard drive space.
A 20GB hard drive with at least 15GB free space.
Yes, you can delete windows 7 by formatting your drive, but all of your files will be gone. If you have two hard drives, you can either copy your data from one drive to the other or put xp/vista on the second one and use the windows 7 drive as a slave.
Yes. Actually, there is no need to remove the hard drive. You can format the existing hard drive and install XP on it as well. Note: Yes, you can there is no need to remove the hard drive. You can format the existing hard drive and install XP. and also you can install both opreting system single computer. XP and vista both.