Currently there are some issues with skinning this control through the VisualStyleBuilder and it is not available for selection. It will be put back in the list as soon as they are fixed.
Most of the skins use background images for transparency and gradients, but the new skins (currently Glow and Silk) use CSS3 gradients. Currently, there is no unified way of creating them with CSS3, because each browser has its own implementation of the property, if it has one at all. This means that customized gradient backgrounds in these skins can have issues and may need manual tweaking after the skin is exported from the tool.
The Visual StyleBuilder is a complex developer tool and targets modern browsers. Its interface and functionality may have some issues under older browsers(e.g., IE7) and we advise using the latest version of a modern browser with this tool.
The tool's interface consists of many tabs that expose the different aspects of tweaking a skin. Before navigating between the mall changes must be saved or they will be lost.
The name of the new skin is chosen in one of the first steps of the wizard-like interface and cannot be changed at a later stage without losing all the changes that have been made so far. We advise that the name the skin should be chosen beforehand to avoid manual find-and-replace operations later.