I have Ubuntu on my laptop. I want to install WinXP. I can prepare space oh HDD. I have i386 of WinXP installation disk. As I understand I can install running i386\winnt.exe but from DOS, so how can I put DOS on my prepared disk?
This is only theory - I haven't tried it out, and there may be some tricky steps involved in the setting up:
You could format your new partition as VFAT, then copy the files you need (the i386 dir) plus the required parts of FreeDOS onto it.
Then you could tweak your Grub setup to include your new filesystem to boot from, then reboot into FreeDOS.
From there you should be able to run the Windows installation program.