Check out Carbon (http://get-carbon.org/) for a much more capable powershell automation libary.

Install via nuget (http://nuget.org/List/Packages/PSHostsFile). Or run .\build.ps1 and use the PSHostsFile.dll.

Powershell:

import-module .\PSHostsFile.dll
        
get-HostsFileEntry
remove-HostsFileEntry <hostName>
set-HostsFileEntry <hostName> <Address>

C#:

using PSHostsFile;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            foreach (var hostsEntry in HostsFile.Get())
            {
                System.Console.WriteLine("Have host {0} - {1}.", hostsEntry.Hostname, hostsEntry.Address);
            }

            HostsFile.Set("foo.example.com", "127.0.0.1");  //  Add or update the hosts file entry for foo.example.com
            HostsFile.Set("another.example.com", "127.0.0.1");
            HostsFile.Remove("another.example.com");  //  Remove a hosts file entry
        }
    }
}