What is the difference between these two declarations?

[2MuchRiceMakesMeSick]

[DllImport("user32.dll")]
public static extern int FindWindow(string lpClassName, string lpWindowName);

[DllImport("user32", EntryPoint = "FindWindowA")]
private static extern IntPtr FindWindow(
[MarshalAs(UnmanagedType.LPStr)] string lpClassName, 
[MarshalAs(UnmanagedType.LPStr)] string lpWindowName);