Looking to install Windows Vista on your PC, but don't want to get rid of Windows XP? In the following simple solution, I show you how to install Windows Vista alongside an existing installation of Windows XP. Once you have completed these instructions, you will be able to dual boot Windows XP and Vista. During system startup, you will be able to select to boot from either Windows XP or Windows Vista. In addition, both Windows XP and Windows Vista will be installed on the same hard drive, eliminating the need to install Windows Vista to a second hard drive.
How to Install Windows Vista alongside Windows XP on the same drive:
Installing Windows Vista on the same drive as an existing Windows XP installation.
Download the GParted ISO, burn it to a CD and boot your PC from the CD
At the GParted boot screen, select (auto-configuration) and press Enter
During boot, just press Enter when prompted to select the keymap and Enter again for language settings
Once GParted has loaded, right click on the main Windows XP NTFS partition (I.E. /dev/hda1) and select to Resize/Move
Next, using the slider, reduce the partition size to free up enough room (10GB+) to install Windows Vista, then click Resize/Move
Next, in order to apply the changes and resize the partition, click Apply. GParted will ask you to confirm the changes, click OK and wait for the process to finish
Once the partition has been resized, remove the GParted CD and shutdown your Computer
Insert and boot from your Windows Vista DVD, select your language and then select the option to Install now
Next, continue until Windows Vista prompts you on where to install. Select the Unallocated space option and click Next
Now simply follow any onscreen instructions to complete your Windows Vista installation.
After the installation of Vista is complete, the Vista boot manager will allow you to start Windows XP or Vista as is seen in the screenshot below: