Using C# class library in silverlight project

Hi,
I am new to silverlight and need help in following regards.
I have created a class library in c# which uses System.data.sqlclient namesapce to connect to data and retrive results. I want to use this dll into my silverlight project. I tried to add this dll reference but it gives error saying the dll cannot be added as its not build against silverlight runtime.
I created a silverlight class library but it do not allow sqlclient namespace.
How to resoolve this?
Regards.
Dilip