Here are some samples:
Actually, a more cross-platform way to make a beep sound is to call Microsoft.VisualBasic.Interaction.Beep() (add a reference to the Microsoft.VisualBasic.dll in the GAC or do "import Microsoft.VisualBasic from Microsoft.VisualBasic"). This is supported in both .NET and Mono.
Here is another example with the EntryPoint specified as a named parameter. Useful I guess if you want to use a different name for the dll call.
For further information, see: