After two days of messing with this I've found a solution to my
problem. Here it is for anyone else who runs into this issue:

Added this public method to my form and called it before the Show
method:

Public Sub FixModalDialogBug()
 ' Make sure the outlook window is disabled while this dialog is open
 Dim hwnd As Long

 hwnd = FindWindow("ThunderDFrame", Me.Caption)
 If (hwnd <> 0) Then
   SetWindowLong hwnd, GWL_HWNDPARENT, FindWindow("rctrl_renwnd32",
vbNullString)
   SetForegroundWindow hwnd
 Else
   MsgBox "Couldn't find the window handle to fix the outlook modal
dialog bug!", vbInformation, Me.Caption
 End If

 ' Center this dialog over the outlook window
 CenterMeOverOutlook
End Sub

Public Sub CenterMeOverOutlook()
 Dim olWidth, olHeight As Integer

 olWidth = Outlook.Application.ActiveExplorer().Width
 olHeight = Outlook.Application.ActiveExplorer().Height

 Me.Left = (olWidth / 2) - (Me.Width / 2)
 Me.Top = (olHeight / 2) - (Me.Height / 2)
End Sub

You need these declarations for the win32 api calls:

Private Declare Function SetForegroundWindow Lib "user32" _
 (ByVal hwnd As Long) As Long
Private Declare Function FindWindow Lib "user32" Alias "FindWindowA" _
 (ByVal lpClassName As String, ByVal lpWindowName As String) As Long
Private Declare Function SetWindowLong Lib "user32" Alias
"SetWindowLongA" _
 (ByVal hwnd As Long, ByVal nIndex As Long, ByVal dwNewLong As Long)
As Long

Private Const GWL_HWNDPARENT = (-8)