将WinForm应用程序限制为具有多个实例的一个进程

We have a WinForms application in C# 3.5 (SP 1). We would like to restrict the application to one process in memory with multiple window instances. We are not looking for an MDI approach, but to have separate main form instances without launching multiple application processes. We have a WinForms application in C# 3.5 (SP 1)