Cast to Anonymous Type

To quote MSDN:

An anonymous type cannot be cast to any interface or type except for object.

Instead of casting to your custom type try using dynamic type.

Your event handler would look something like this:

private void cmdOK_Click(object sender, EventArgs e)
{
    dynamic option = bsOptions.Current;
    if (option.Id == 1) { doSomething(); }
      else { doSomethingElse(); }
}

Note, as per the comment, I'd just like to point out that I too recommend using a real type when you need to pass it around the program like this. Anonymous types should only really be used locally in a single method at a time (in my opinion), but anyway, here's the rest of my answer.

---

You can do it using a trick, by tricking the compiler into inferring the right type for you:

using System;

namespace ConsoleApplication4
{
    class Program
    {
        static void Main(string[] args)
        {
            var a = new { Id = 1, Name = "Bob" };
            TestMethod(a);

            Console.Out.WriteLine("Press enter to exit...");
            Console.In.ReadLine();
        }

        private static void TestMethod(Object x)
        {
            // This is a dummy value, just to get 'a' to be of the right type
            var a = new { Id = 0, Name = "" };
            a = Cast(a, x);
            Console.Out.WriteLine(a.Id + ": " + a.Name);
        }

        private static T Cast<T>(T typeHolder, Object x)
        {
            // typeHolder above is just for compiler magic
            // to infer the type to cast x to
            return (T)x;
        }
    }
}

The trick is that inside the assembly, the same anonymous type (same properties, same order) resolves to the same type, which makes the trick above work.

private static T CastTo<T>(this Object value, T targetType)
{
    // targetType above is just for compiler magic
    // to infer the type to cast value to
    return (T)value;
}

usage:

var value = x.CastTo(a);

But we're really pushing the limits here. Use a real type, it'll look and feel cleaner as well.

In C# 3.0, this is not possible. You'll have to wait for C# 4.0, which allows accessing properties at runtime using "dynamic" variables.