ClientUI includes designer extensions that allow you to work with the user interface elements in Expression Blend designer. For example: you can add a dropdown button in the toolbar control through context menu, select and expand the dropdown button to see its items, and rapidly add the subsequent menu items into the dropdown button.

I'd like to suggest you to check the ClientUI documentation with topic: "Working with ClientUI Controls in Expression Blend Designer". This topic highlights the key features available in ClientUI designer extensions such as:

• Assets Registration
• WYSIWYG Design Experience
• Context Menu
• Activate/Show on Selected
• Layout Adorner
• Default Content
• Property Category and Description
• Related Walkthroughs

Should you have further problem regarding how to use ClientUI with Blend, please feel free to let us know. Thank you and have a nice day.

think you!

And I have another question. how to make the client skins like the attachment with intersoft? 

You can start to apply styling and templating to custommize the appearance of ClientUI based on the design. Following articles in ClientUI documentation should helps you to give an overview of styling and templating aspects of the application and shows how to change the style of UXWindow by using designer tool.

• Styles and Templates Overview
• Walkthrough: Style a Window in Blend Designer

Hope this helps.