DotProject themes are not distributed much, because there are not many developers who are eager to create such themes. The dotProject script comes with three themes pre-installed and the developers believe this is more than enough for the clients.
Anyway, themes can be edited if you have some basic knowledge of php/html.The theme content can be found inside your dotProject install directory under the style folder.You need to copy one of the folders with another name (the one of the theme you are going to create).Then you can edit the files inside so that they suit your needs.
Changing dotProject theme is easy:
1. Log in your dotProject's admin area.
2. Click on System Admin.
3. Select Default User Preferences.
4. Select from the drop-down menu besides the User Interface Style label your theme name.
5.Click on Submit at the bottom of the page.
If you happen to find or purchase a theme, just extract the content of the archive they provide you with inside the style folder and then follow the steps listed above to activate it.