|If you want to be able to run Vista and XP......|
Install a virtual machine program in Vista, such as the apparently very good Microsoft's free Virtual PC 2007. Then install XP in the virtual machine program.
(Lots of info available about Virtual PC 2007 on the Microsoft web site, and on the web).
Installing XP and SATA drive controllers, SATA drives; the SATA drive controller bios settings.
See response 2:
I DO NOT recommend that you use the Windows operating system's built in multiboot feature to dual or multiboot XP and Vista or Windows 7 !
You are supposed to install the older Windows operating system first, but you CAN get the Windows Vista or Windows 7 multiboot feature to work when it was installed first when there is a working XP installation on another partition if you follow certain procedures.
However, by default, whenever you boot XP, ALL the System Restore restore points are DELETED in Vista and/or Windows 7, every time you boot XP !
If that concerns you (you may eventually NEED to try using a previous System Restore restore point, rather than installing Vista or Windows 7 from scratch) ......
If you have one of the more expensive versions of Vista or Windows 7 - e,g. Ultimate, that has the bit locker (bitlocker ?) feature, you can use that feature to get around that problem.
If you DO NOT have a more expensive Vista or Windows 7 version that has the bit locker (bitlocker ?) feature, then you're much better off using a third party multi-boot program that is Vista and Windows 7 "aware" (compatible) to multiboot your operating systems, instead of Vista's or Windows 7's built in multiboot feature.
E,g. I use BootIt N.G. to dual boot (XP) MCE 2005 and Vista, and there is a video tutorial on the maker's web site about how you HIDE the partition Vista's or Windows 7's Windows itself was installed on while booting XP. It's not free but it's reasonably priced. .
If you DO choose to have both Vista and XP available, via dual or multibooting, you probably need to SHRINK at least one Vista partition to provide un-allocated space to install XP on
The HELP documentation about how to use the built ability of Vista to expand - EXTEND - or contract - SHRINK - an existing partition without losing the data on the partition.
The same probably applies to Windows 7.
It's NOT in Help and Support (at least it isn't in Vista) - it's in Disk Management's Help.
Control Panel - Classic View - Administrative Tools - Computer Management - Disk Management
In Windows 7......
Control Panel - display as Large icons or Small icons - Administrative Tools - Computer Management - Disk Management
RIGHT click on the drive letter of the existing partition, click on Help.
Manage Basic Volumes
Extend a Basic Volume
Shrink a Basic Volume