Plugin download [link]
The link is in the video description, to find it easier you can use Ctrl+F and find "bowlroll.net". The video also show how to use some advanced features of the plugin but it's too confusing for me.
To install plugin, download the file, extract it, rename the folder "skirt plugin" and put it in the following folder: your PMD editor folder>plugin>user>skirt plugin.
The plugin only works with PMDE version 1.37 or higher, I've tried with 1.00 and the english version but they didn't work.
I've been very hesitant to make character with skirt and long coat because skirt rigging is a pain and this plugin is a life saver. I love it so much and want to share it with everyone ^^