Hello Bartosz Rychert,
Have you installed the Silverlight Tools from here: http://www.microsoft.com/downloads/details.aspx?FamilyID=bf5ab940-c011-4bd1-ad98-da671e491009&displaylang=en.
Make sure that you have the items on the attached screenshot (the two SL3 items only if you want to have SL3 and SL4 at the same time). Missing the Silverlight Tools may results in missing the template for Silverlight projects.
Please let me know if you are still having problems.
the Telerik team
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