Sorry, but I dropped out at Warp3.
If I were to hazard a guess it would be this. PARTITION ONLY what you need for Warp4, install Warp4 and then let XP partition it's own space and install there.
I will not tell you how many want to try to add such an OS as you noted after XP but will share I have mild success in the method I noted above.
I have an 80 GB hard drive running Windows XP Home SP2 on the primary partition (C:\). On the secondary partition is some unneeded back-up info and some media (D:\). I was wondering if I could format (D:\) and make it OS/2's file system, then proceed to dual boot with an installation of OS/2 Warp 4. Anyone have a suggestion?