Name 'ConfigurationManager' is not declared in VB.Net 2.0

in a ASP.Net 2.0 web Application, to get a connection string from Web.config, you would write:
ConfigurationManager.ConnectionStrings("DB").ConnectionString

trying to do the same in a Windows application, would give you the error :
Name 'ConfigurationManager' is not declared
even you did import "System.Configuration"...

well, after searching i found that you need to add reference to "System.Configuration.dll" : under Project > Add refrence > .Net > select System.Configuration