[For those who might experience similar problems and could find this information useful]
It is enough to specify attributes:
Code:
[assembly: System.Windows.Markup.XmlnsDefinition("http://www.springframework.net/wpf", "Spring.Context")]
[assembly: System.Windows.Markup.XmlnsDefinition("http://www.springframework.net/wpf", "Spring.Expressions")]
Copying of schema into the VS folder does not take effect and instead of this the attributes can be applied to the integration assembly. Everything works perfectly 
What I see, the original Spring.Wpf.2005.Orcas project does that. Well, I didn't mention that I've taken the source code only and have built the assembly project from scratch - that was the reason of my problems...