VS 2005 did include a designer for XSD-Files.
Where i can find the version for VS 2008?
I only found a preview version for VS 2008 beta 2.
I would recommend against using the dataset editor for an XML schema, there is a reason Microsoft have stopped supporting the schema designer from VS 2005.
We have had no end of trouble with the schemas that were produced from the VS 2005 schema designer, so much so that we have just recently had to re-design them.
I would either use the basic XML text editor and the XML document outline or I would look at XML Spy. This is what we have just purchased (after using the free trial) to validate and re-do our schemas.
In VS2008, AFAIK the primary tool is the xml editor, with the assistance of the "XML Schema Explorer" toolbar. Other than that, you have the "Dataset Designer", but this risks adding dataset-specific elements.
A post from an MSFT support head is here; there was rumour of an out-of-band release for this, but I haven't seen anything.
Microsoft dropped the schema editor with the release of 2008. I could never realy understand the version released in the older versions, so it was no great loss. They did release a schema editor in 2007, but it was very low level, not much better than a test editor. See MS Schema Designer.
The integration XML Spy offers is a bit clunky, and doesn't seem to fit well into visual Studio.
We use Liquid XML Studio, which integrates pretty seamlessly with Visual Studio, and makes it so much easier to author XML Schemas. See XML Schema Editor Visual Studio Plugin
Here you can find the same issue as a bug report.
Unable to view in designer mode (VS2008) the XSD file
More info about the topic you can find here
Right click your XSD file and choose "open with..." then select Dataset Editor.
(If you don't already have an .XSD file, create an empty text file and name it with XSD extension)
来源：https://stackoverflow.com/questions/746673/xml-schema-designer-for-visual-studio-2008