A couple of days ago I successfully installed Windows Longhorn 4051, also known as the PDC build. I previously dual booted Windows XP Professional and Mandrake Linux 9.2, but with Novell purchasing both Ximian and SuSE, I decided to switch to SuSE 9. So today I got it installed with GRUB as my bootloader. I now triple boot SuSE Linux 9, Windows Longhorn, and Windows XP Professional. If you are looking to do the same thing, here are the steps:
1) Install Windows XP
2) Install Windows Longhorn
3) Edit the boot.ini to include both Windows XP and Longhorn (longhorn overwrites it during install)
4) Install Linux
This order of doing things will allow the bootloader you choose during Linux install to detect both of your Windows operating systems and make entries for them.
So far SuSE 9 works very smoothly, no major problems. I much prefer the look of Mandrake “out of the box” but after installing the recently released Ximian Desktop 2 for SuSE 9, things are perfectly fine again! Now all I have to do is wait for MonoDevelop…
MasterMaq's Blog 
How can I do the same thing that you explained here with Windows XP Pro, Windows Server 2003 and Red Hat Enterprise Linux 3 all on seperate hard drives.
Please contact me at ghill0463.hardware1@zoemail.net
Thank you.
I have a Windows XP notebook. What is the simple way to triple-boot with W2K server and
Red hat Linux 8.0 without reinstalling my XP?
Microsoft advise the installation of W2K before XP. Appreciate if you know the trick
for any work-around.
Contact me at lokewh111@yahoo.com.sg
John