Win xp64 also runs 32 bit applications (badly but runs) so you could easily get a masm ,nasm , fasm or other compiler and start coding without problems =).

LOL !
my idea is a newbie should be new , why he should learn win32 or 32 bit assembly.so
http://www.jorgon.freeserve.co.uk/Go.../Hello64World1

is the first program.and toochain is goAsm , I thik NASM is also supports.

But in your thread you asked 16-bit application to this os , yes 16-bit windows or dos applications ? both are not working under
xp 64 bit , then you need to install dos-box if you really want to
dig into the old computing platform. good nothing you learn will
be a waste.