From B2evolution

In order for your skin to be listed at skins.b2evolution.net it has to meet a few requirements.

1. Your skin should validate as XHTML. The version you use is not as important as the fact that it validates. See also Validate as XHTML.
2. Take a screenshot of your skin and put it in your skin folder, calling it skinshot.jpg. The image should be 240x180.
3. Include a skininfo.html file in your skin. Indicate the version(s) of b2evolution that your skin is meant to work with. You can also put your credits and a description of the skin in there, including what features the skin includes. These will be posted with your skin to allow users to search the directory and find your skin.
4. Zip your skin folder up and send it as an attachment to skins at b2evo dot net.

The final decision about whether a skin is posted rests with the b2evolution team.