You are correct about me needing more rest.

I'm still having some problems. The code runs fine for the meat of the
process however when the application ends, I get the following error:

The instruction at "0x00000000" referenced memory at "0x00000000". The
memory could not be "read".

I'm assuming this is some sort of memory allocation error or such. Where am
I not clearing things properly?

Below is the code I am using for a console application:

Imports System.Drawing.Printing
Imports System.Runtime.InteropServices

Module Module1

   <StructLayout(LayoutKind.Sequential)> _
   Public Structure DRIVER_INFO_6
       Public cVersion As Int32
       Public pName As String ' QMS 810
       Public pEnvironment As String ' Win32 x86
       Public pDriverPath As String ' c:\drivers\pscript.dll
       Public pDataFile As String ' c:\drivers\QMS810.PPD
       Public pConfigFile As String ' c:\drivers\PSCRPTUI.DLL
       Public pHelpFile As String ' c:\drivers\PSCRPTUI.HLP
       Public pDependentFiles As String '
       Public pMonitorName As String ' "PJL monitor"
       Public pDefaultDataType As String ' "EMF"
       Public pszzPreviousNames As String
       Public ftDriverDate As FILETIME
       Public dwlDriverVersion As Int64
       Public pszMfgName As String
       Public pszOEMUrl As String
       Public pszHardwareID As String
       Public pszProvider As String
   End Structure

   <DllImport("winspool.drv", EntryPoint:="OpenPrinterA", _
       SetLastError:=True, CharSet:=CharSet.Ansi, _
       ExactSpelling:=True, _
       CallingConvention:=CallingConvention.StdCall)> _
       Public Function OpenPrinter(ByVal pPrinterName As String, _
                                   ByRef phPrinter As IntPtr, _
                                   ByVal pDefault As Integer _
                                   ) As Boolean
   End Function

   <DllImport("winspool.drv", EntryPoint:="ClosePrinter", _
       SetLastError:=True, _
       ExactSpelling:=True, _
       CallingConvention:=CallingConvention.StdCall)> _
       Public Function ClosePrinter(ByVal hPrinter As IntPtr) As Boolean

   End Function

   <DllImport("winspool.drv", EntryPoint:="GetPrinterDriverA", _
       SetLastError:=True, _
       ExactSpelling:=True, _
       CallingConvention:=CallingConvention.StdCall)> _
       Public Function GetPrinterDriver(ByVal hPrinter As IntPtr, _
                                   ByVal pEnvironment As String, _
                                   ByVal Level As Integer, _
                                   ByVal pDriverInfo As IntPtr, _
                                   ByVal cdBuf As Integer, _
                                   ByRef pcbNeeded As Integer _
                                   ) As Boolean
   End Function

   Sub Main()
       Dim sName As String

       For Each sName In PrinterSettings.InstalledPrinters
           Console.WriteLine(sName)
           Dim bVirtual As Boolean = IsPrinterVirtual(sName)

           Console.WriteLine(vbTab + "IsVirtual?: " + bVirtual.ToString +
vbTab)

           Console.ReadLine()
       Next

       Console.Write("Done: ")
       Console.ReadLine()
   End Sub

   Public Function IsPrinterVirtual(ByVal printerName As String) As Boolean
       Dim hPrinter As IntPtr = IntPtr.Zero
       Dim InfoPtr As IntPtr = IntPtr.Zero
       Dim lBytesNeeded As Integer = 0
       Dim bReturn As Boolean = True

       Try
           If Not OpenPrinter(printerName, hPrinter, 0) Then
               Console.WriteLine("Could not open printer")
           End If

           ' Allocate an unmanaged buffer in which to store the returned
structure
           ' InfoPtr is the pointer pointing to that buffer
           InfoPtr = Marshal.AllocHGlobal( _
                   Marshal.SizeOf(GetType(DRIVER_INFO_6)))

           GetPrinterDriver( _
                   hPrinter, vbNullString, 6, InfoPtr, _
                   0, lBytesNeeded)

           GetPrinterDriver( _
                   hPrinter, vbNullString, 6, InfoPtr, _
                   lBytesNeeded, lBytesNeeded)

           If Not ClosePrinter(hPrinter) Then
               Console.WriteLine("Could not close printer")
           End If

           Dim Info As DRIVER_INFO_6
           Info = CType( _
                   Marshal.PtrToStructure( _
                   InfoPtr, GetType(DRIVER_INFO_6)), _
                   DRIVER_INFO_6)

           If Info.pszHardwareID = Nothing Then
               bReturn = True
           Else
               bReturn = False
           End If

           Marshal.FreeHGlobal(InfoPtr)

       Catch ex As Exception
           Console.WriteLine(ex.Message)
       End Try

       Return bReturn

   End Function

End Module