It depends on how many clients will request this feature. We do not plan it for the upcoming release of RadControls for Silverlight this November.
What do you mean by "I am also wondering if it is possible to use this combobox inside a textbox?" ? Probably if you describe what do you need to achieve, I will be able to give you some suggestions.
Regarding the styling of RadComboBox - we provide a simple application, that demonstrates how to modify the skins of all RadControls for Silverlight. To find it go to:
Expand RadControls for Silverlight and download Telerik_Windows_Controls_Blend_Trial.zip. The application can be opened in Expression Blend and used to skin all controls. Let me know if you have problems with it.
the Telerik team
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