Please help with USING command

Hello,

I'm new to C# but I'm programming for few years in Java, am using MS VS 2008. I need to write application for DNS lookups. I found pretty cool add-on for C#, class package, library or however it is called on this link: http://www.codeproject.com/KB/IP/DNS_NET_Resolver.aspx

I downloaded Project source and I found DNS folder with classes for DNS manipulation. I had copied that folder to my project folder, but now i don't know how to implement that in my project. It says that library should be included with: "using Heijden.DNS;" but when I type that I get an error: " The type or namespace name 'Heijden' could not be found". I know I'm missing something but I don't know what. Please help me.... :(