Advantages of using the function directly in your program instead of calling rundll32.exe are meanful error codes and no external process needs to be called resulting in more control.

C# Signature:

[DllImport("printui.dll", SetLastError = true, CharSet = CharSet.Unicode)]
private static extern void PrintUIEntryW(IntPtr hwnd, IntPtr hinst, string lpszCmdLine, int nCmdShow);

Sample Code:

Get available commands in dialup box

PrintUIEntry(IntPtr.Zero, IntPtr.Zero, @"/?", 0);

Add per machine printer connection (the connection will be propagated to the user upon logon):

PrintUIEntry(IntPtr.Zero, IntPtr.Zero, @"/c \\machine /ga /n\\server\queue", 0);

Delete per machine printer connection (the connection will be deleted upon user logon):

PrintUIEntry(IntPtr.Zero, IntPtr.Zero, @"/c \\machine /gd /n\\server\queue", 0);