16-bit, 32-bit etc are the types of operating systems. it depends on the hardware architecture. earlier windows (version 3.11) were 16-bit while the present day windows xp comes in both 32-bit and 64-bit depending upon the hardware platform you wish to install it on.
anyways, to begin installation of windows xp from dos mode, navigate to the i386 folder and type "winnt" (without the quotes) to begin setup.