Several workarounds have been proposed for MKW-XP trouble. This is  
reportedly the simplest and most effective to date.

Mike Wren <mikew@etree.org> wrote:

To run mkwACT in Windows XP, change the compatibility mode for mkwACT to
"Windows 2000" by:

* Right-click on the link to mkwACT in the start menu or desktop
* Click properities
* Click the Compatibility tab
* Click the checkbox for "Run this program in compatibility mode for:
* In the pulldown menu, choose "Windows 2000"

br0thercr0w <br0cr0w@etree.org> added:

That should have it running 99% correctly (i still haven't been able to
get it to let me batch files to it by highlighting a large group of files
and right clicking on them and choosing to "convert to wav" or "encode to
shn", but drag & drop still works in batches fine and it otherwise works as
it always has).