1. Backup your important files on the partition which has Windows XP on it. Most probably it is first partition (C:). This is done to remove XP and install Vista.
2. The steps shown below would wipe out and format all data on first partition (or any partition you choose to install Vista)
You must have Windows Vista DVD for installation of Vista :
1. Set boot preferences in your computer BIOS, so that DVD drive is the first, hard disk is second boot device. If you have a newer PC, you dont have to change BIOS settings but press F12 during computer boot and then select DVD drive as booting device.
2. Place DVD in your DVD drive.
3. Your computer would detect DVD and you would see Press any key to boot from DVD...
. Press any key to run Vista setup.
4. When it asks which type of installation do you want
5. Next you will have to choose a partition. Choose the same partition as you have used for Windows XP for example Disk 0
which is C: drive. This action would wipe out your C: drive. Click Next when you select the partition. Choose to full format in NTFS.
6. Rest of the installation is easy, you dont have to do anything.
Just remember to:
1. Backup your databefore you install Vista
2. Steps 5 is very important to remove XP and install Vista.
For more information : http://www.petri.co.il/install_windows_vista.htm