How to dual-boot Vista and XP with Vista installed first
1. In Start Search type diskmgmt.msc. Alternatively you can boot into the Vista DVD and start DISKPART as outlined in the previous section.
2. In Disk Management right-click a partition and select Shrink Volume. Enter the amount of space to shrink in MB (approx. 10 GB) and click Shrink. Then close Disk Management.
If you use DISKPART:
a) Type List Volume
b) Type Select Volume X; X being the NTFS Partition you want to shrink to create free disk space
c) Type shrink desired=10240
d) Type Exit
e) Click the cross on the top right corner of the install screen.
f) Click Yes to confirm that you want to cancel the install. Eject the Vista setup DVD
3. Boot your computer with your Windows XP setup DVD and install XP onto the free space
4. Download and install the Microsoft .NET Framework Version 2.0 Redistributable Package (x86)
5. Download and install EasyBCD
6. Launch EasyBCD
7. Click Add/remove Entries, and then change the drive to the partition where you installed XP. In Type change the dropdown menu to Windows NT/2k/XP/2k3
8. Change Name to Windows XP Home or to Windows XP Professional, whatever you have
9. Click Add Entry, and the click Save
10. Click Manage Bootloader. Select Reinstall the Vista Bootloader. Click Write MBR
11. Exit EasyBCD and restart your computer