To add windows support to TagLib, download this zip and unzip it in the top-level directory of the 1.3.1 release from the TagLib website. It will make a directory called ‘win32′ with in it project files for Visual Studio .Net 2003 so that you can compile dll’s directly from source.
If you don’t want to compile yourself but just want a binary of the dll (in debug and release versions) and the documentation, download this.
If you use any of these download or are having problems with them, contact me at roel dot vanhout at gmail dot com. I’d like to know if there are any people actually using this - if not, I won’t be doing updates unless I need them myself.
Also if you want support for other versions of VS, let me know.

Update 18/3/2007: The files above have been lost in some reorganisation on my web host over the last few months, and I don’t use TagLib anymore because I needed to support id3v2.3 (which is used by Windows Media Player and other popular players) There are a few other people who posted about their efforts to get TagLib running on Windows, see http://metz.gehn.net/downloads/, https://launchpad.net/~luks/+branch/taglib/win32 and http://www.titus-dev.com/index.php?mod=Code%20Library&parent=1&action=view_proj&id=18.