It don't have to do much with ajax(in th sense that ajax is generally used for dynamic client side interactions)
You need a server side script which takes the input and converts it to doc.
You may use something like openoffice and python if it has some interface
see http://wiki.services.openoffice.org/wiki/Python
or on windows you can directly use Word COM objects to create doc using win32apis
but it is less probable, that a windows server serving python :)
I think better alternative is to generate PDF which would be nicer and easier.
Reportlab has a wonderful pdf generation library and it works like charm from python.
Once you have pdf you may use some pdf to doc converter, but I think PDF would be good enough.
Edit: Doc generation
On second thought if you are insisting on DOC you may have windows server in that case
you can use COM objets to generate DOC, xls or whatever see
http://win32com.goermezer.de/content/view/173/284/