Below you can see the skin elements of of the control bar. As you can see, they consist of small images which you can easily change. The best way to start a skin is by copying an existing one. In the installation zip (s3mediapro.zip) is a folder called: skins and in that folder is a sub folder called Beelden. I used that one as a basis for Polished Metal, included in this module.
- volumeSlider (Rail, Buffer, Progress)
All it takes is to open all those images in an image editor and adapt it to your own design.
Just keep the names as they are and you will be fine.
More information can be found in the official tutorial: http://developer.longtailvideo.com/trac/wiki/Player5Skinning