When i was approached by one of my friend to configure his laptop so that Windows XP could run alongside Windows Vista…i thought it would be a child’s play ! The Laptop came with a pre-installed Windows Vista. Having tried my hands numerous times over making systems multi-boot , i was confident of sailing through the situation .
Little did i knew that ignorance on my part would screw up his system. Here’s an account of what i did…hope that you don’t fall into a similar pit !!! I made the CD-ROM as the first boot device & put up a XP installation disk into it. I modified the partitioning scheme to ensure that XP installation does not take place on a partition on which Vista Resides.The installation went of smoothly as expected but upon restarting the system the system booted into XP automatically & didn’t gave an option to select an OS.The poor guy was left with a screwed system.
Here’s an excerpt from Microsoft which demystifies the problem :
“Earlier versions of the Windows operating system are incompatible with the new Windows Vista startup method. Windows Vista uses a new Boot Configuration Database (BCD) store. This store contains a boot menu and all the information about operating systems that are installed on the computer. Therefore, a Boot.ini file that is from an earlier version of the Windows operating system cannot be used to start Windows Vista.
When you install an earlier version of the Windows operating system on a Windows Vista-based computer, Setup overwrites everything from the MBR, the boot sector, and the boot files. Therefore, the earlier version the Windows operating system loses forward compatibility with Windows Vista.”
For all those Guys who are planning to install Windows Vista alongside XP, just keep the above in mind before attempting to configure the system.
Scribbles of a Chaotic Mind 
I have been let down by the Windows Vista OS ! Plethora of options are available for performing most basic operations, leaving the end user completely confused.It may be the most stable & secure OS of the Windows family but it definitely lacks the ease of use Windows XP provided to the users.
well friend the problem u have faced, definitely leaves most of the people amazing for the reason, but yeah i would like to bring to light that its not impossible to dual boot windows xp with vista, what u gotta do is go the other way round, i.e. install xp first, and then install vista, and it work out… just give it a try.. meanwhile the users of vista, what do u people think is it worth upgrade from xp, considering the amount of resources it utilizes?