There are several tutorials on YouTube which will show you exactly how to remove a partition. Removing a hard drive partition on Windows Vista will create an empty space that you can use to install a new partition. Be aware that it will also delete all data that is on the partition.
You can add/remove/modify partitions on your hard drive with a program called Partition Magic.
There are many ways, but the easiest is to use a Windows 7 installation disk to delete the partition.
See this link for step by step instructions http://www.addictivetips.com/windows-tips/extend-or-expand-volume-of-windows-partition-in-vista/comment-page-1/
You have to create at least one more partition for Vista. If you install Vista on the partition where XP is installed Vista will delete XP. To avoid such problem you have to have one more partition. When you do that just start the Vista installation process from XP and choose just created partition for Vista.
No your windows 7 will not deleted
You cannot format the drive / partition that Windows Vista is currently running on while it is running. You will need to boot from either a partition utility disc, such as GParted, or the install disc of the operating system you want to install, and format the drive from there.
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
Of course.
For complete instructions on how to remove windows vista check: www.removevista.com
Of course, backup all your files to an external hard drive and perform a clean install with your Vista disk. They only make it easy to upgrade never downgrade. If you do not have an external hard drive, create a disk partition to use as your file backup.
If you have the windows install disc, you can insert it, restart your computer and press any key when it tells you to. This will boot from the DVD and enter the Windows Setup. From there, it will show you a list of partitions on your hard drive before you install windows. Choose the partition on which Vista is installed and click "Delete" under advanced options. The partition will be formatted. If you want to install a fresh copy of Windows Vista, you can do so now. If not, exit windows setup and install whatever OS you want to use. (Make sure you BACK UP your files before formatting - once you format the partition, you can NEVER get the files back.)
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.
There's no such thing as Windows XP format or Windows Vista format. You should check however if your external hard drive uses an NTFS or FAT32 partition table. You can see that by right-clicking the drive (C, D, E, ..) and clicking properties. If it uses NTFS it will be no problem for Vista. If it's FAT32, then google for a way to convert it to NTFS. No big deal.