To install NuGet in Visual Studio 2010 open the Extension Manager dialog from the top-level Tools menu, and search for NuGet in the Online Gallery. Download and install from here.
To add XML-RPC.NET to a project, open the Add Library Package Reference from the top-level Tools menu, and search for "xml-rpc" from Nuget official package source in the Online section. When the xmlrpcnet package appears click on the Install button and the current version of the CookComputing.XmlRpcV2 assembly will be automatically downloaded and added as a reference in your project.
I'm currently working on the next release of XML-RPC.NET and when it is ready (delayed by a bout of 'flu last month) I'll update the NuGet Gallery with the new version. I'll blog about the features of the upcoming release tomorrow.