C# Definition:

private delegate bool EnumWindowsProc(IntPtr hWnd, IntPtr lParam);

VB Definition:

Private Delegate Function EnumWindowsProc(ByVal hWnd As IntPtr, ByVal lParam As IntPtr) As Boolean

Notes:

If you're going to use the lparam to return a by-value result (such as the hwnd of a window you are looking for), you'll want to send lparam by reference:

C#:

private delegate bool EnumWindowsProc(IntPtr hWnd, ref IntPtr lParam);

VB.NET:

Private Delegate Function EnumWindowsProc(ByVal hWnd As IntPtr, ByRef lParam As IntPtr) As Boolean