Form の拡張スタイルに WS_EX_TOOLWINDOW を適用してあげれば、Alt + Tab に表示されなくなると思います。
Class FormBorderStyleをNoneにしているForm
Private Const WS_EX_TOOLWINDOW As Integer = &H80
Protected Overrides ReadOnly Property CreateParams() As System.Windows.Forms.CreateParams
Get
Dim p As CreateParams = MyBase.CreateParams
p.ExStyle = p.ExStyle Or WS_EX_TOOLWINDOW
Return p
End Get
End Property
End Class
> Class FormBorderStyleをNoneにしているForm > Private Const WS_EX_TOOLWINDOW As Integer = &H80 > Protected Overrides ReadOnly Property CreateParams() As System.Windows.Forms.CreateParams > Get > Dim p As CreateParams = MyBase.CreateParams > p.ExStyle = p.ExStyle Or WS_EX_TOOLWINDOW > Return p > End Get > End Property > End Class