>For example, how can I get myclass2 in namespace2 to access something in myclass1 namespace1?

Try this:

//one.cs
using System;

namespace namespace1
public class myclass1
{
  public string mystring = ""
}

//two.cs
using System;
using namespace1;

namespace namespace2
public class myclass2
{

public static void Main ()
{
///Access namespace1.myclass1 in one.cs here.
myclass1 obj = new myclass1()
Console.WriteLine(obj.mystring);
}

}