The windows binaries for libxml are available at the following URL:

http://www.zlatkovic.com/libxml.en.html

It's the best to use the FTP link:

ftp://ftp.zlatkovic.com/pub/libxml/

There you can download the most recent versions of iconv, libxml2 and libxslt.

Unzip the files, and move the exe and dll files into something like: c:\docbook\tools