Physical machine to virtual machine and place into VirtualBox

I am trying to take a newly created virtual machine and have it run on VirtualBox. I want to create a virtual machine out of my existing machine (Windows 7 Pro 64bit) so I used VMWare's free converting tool in order to create the image. I am having difficulties when I try and load the vmdk file to VirtualBox. I have read posts and many forums that say that you are able to use a vmdk image in VirtualBox but after many attempts I have not been able to do it. I have tried booting off the backup disk and did not work. Anyone tips on how to put a virtual copy of your physical machine (Windows 7 Pro 64bit) and get it to boot and run in VirtualBox? Any tips would help. The thing is that all my other VM's work with no problem except the virtual copy of my physical machine.