Windows XP doesn't have a DOS mode.
If you wnat to bring it up in safe mode, press F8 after POST and Before Xp
starts loading. You get startup options.
If you want to get to a command prompt and have a faulty Xp installation
boot off the XP CD. You get recovery mode, installation or other options.
If it is really DOS that you want, use an old 98 startup floppy!
If you don't have a floppy, then USB devices will prove not to be Bootable
as most PC BIOS cannot load specifc driver files for the multitude of USB
peripherals - floppy, CD, HDD, Memory Stick, Camera, Copier /
Printer......the list goes on. How would one manage to get all this info
onto a simple EEPROM. One would not need an operating system, it could all
be resident in BIOS - then it wouldn't be call Basic Input/Output System
would it?