here is a guide, it says 2 do it with vista, but it would work with all OS's
Source
Here is a quick guide to let your PC Dual Boot Windows XP and Windows Vista:
(I will b doing this on my comp very soon)
XP users:
1) Right click 'My Computer' and press 'Manage'
2) Go to 'Disk Management'
3) Create a partition that has more then 10 GB (Vista will be installed on here)
4) Put in your Vista Installation disk (I recomend RC1)
5) Install Vista on the new partition that you made
6) When you turn on your computer, you will see a boot screen where you can select your operating system
Vista users:
1) YOU WILL HAVE TO FORMAT YOUR DRIVE TO INSTALL XP OR THERE WILL BE MULTIPLE ERRORS WHILE INSTALLING!!!
2) Insert the Vista installation Disk and restart your computer.
3) Makesure the disk runs right after the Vista boot screen comes up.
4) Format your drive (YOU WILL LOOSE EVERYTHING)
5) Create a partition that has more then 10 GB (XP will be installed on there) (You should have 2 partitions)
6) Take that disk out and insert the Windows XP installation disk
7) Install it on one of the partitions that you made
8) After you installed XP, restart your computer with the Vista Installation Disk in the Drive
9) Makesure the disk runs right after the XP boot screen comes up.
10) Install Vista on the other partition
11) When you turn on your computer, you will see a boot screen where you can select your operating system
For multiple hard drive users:
1) You can have XP or Vista installed on your computer when following this guide
2) Insert the installation Disk for the Operating system you want to install (Vista or XP)
3) Install it on another hard drive that you have
4) When you turn on your computer, you will see a boot screen where you can select your operating system
If you don't see a Boot Menu when you start up your Computer:
Option 1 (Windows XP and Windows Vista):
1) Boot into either Vista or XP (which ever loads)
1) Right-Click My Computer
2) XP - Click "Avanced"
Vista - click "Advanced System Settings" on the left then go to the "Advanced" tab
3) Click on "Settings" under "Startup and Recovery"
4) Raise the number of seconds next to "Time to Display List of Operating Systems"
5) Press OK
6) Restart
Option 2 (Windows XP):
1) Go to 'My Computer'
2) Click on 'Tools'
3) Click on 'Folder Options'
4) Go to the 'View' tab
5) Check 'Show Hidden Files and Folders'
6) Uncheck 'Hide protected Operating System files'
7) Press 'OK'
8) Go to the root of your hard drive
9) Open the file 'boot.ini'
10) Change the "timeout=n" (n=the number of seconds you want the boot menu to show up. I recomend 30 seconds.
11) Save the file and reboot your computer
Option 3 (Windows Vista):
1) Go the 'Controll Panel'
2) Click on 'Folder Options'
3) Go to the 'View' tab
6) Check 'Show Hidden Files and Folders'
7) Uncheck 'Hide protected Operating System files'
8) Press 'OK'
9) Go to the root of your hard drive
10) Open the file 'boot.ini'
11) Change the "timeout=n" (n=the number of seconds you want the boot menu to show up. I recomend 30 seconds.
12) Save the file and reboot your computer
Boot Menu:
Earlier Version of Windows = Wndows XP
Microsoft Windows Vista = Windows Vista
WHEN YOU ARE USING XP, YOU CAN FORMAT AND/OR DELETE VISTA SYSTEM FILES!!!
WHEN YOU ARE USING VISTA, YOU CAN FORMAT AND/OR DELETE XP SYSTEM FILES!!!
Please note that whatever operating system you boot into becomes the 'C' drive. The other operating system will become the 'D' drive
enjoy
PSP FW 1.5/2.00 
Linear Mode
