I have recently parametrized my ViewModel\'s contructor. Before that, I was doing this in my window:
I have no idea how to pass a contructor-parameter, I think it can't be done (but it would be nice if someone proved me wrong).
What you can do is set properties on your ViewModel, as in
<Window.DataContext>
<vm:MyViewModel MyProperty="Hello" />
</Window.DataContext>
Use an ObjectDataProvider if you want to specify constructor parameters:
<Window.DataContext>
<ObjectDataProvider ObjectType="vm:MyViewModel"
xmlns:sys="clr-namespace:System;assembly=mscorlib">
<ObjectDataProvider.ConstructorParameters>
<sys:String>A string parameter</sys:String>
<sys:Int32>42</sys:Int32>
</ObjectDataProvider.ConstructorParameters>
</ObjectDataProvider>
</Window.DataContext>