Thanks, loukingjr. That article helped me to set up the VM with all the required settings. It still didn't help with getting the VM to recognize the physical DVD drive. So I created a bootable flash drive but had no luck with that, either. But I finally was able to install the 64 bit version on top of the 32 bit version and not lose the activation.
First I created a virtual optical drive in the VM settings. I then clicked on Choose Disk and selected Files of Type RAW, then I navigated to Windows.iso in the OS X file system. Then I went to the System tab and set the boot order to Optical first and Hard Disk second. I turned off my physical DVD drive. When I booted with this configuration it booted from the virtual optical drive. Then I followed the remaining direction in the article you mentioned.
Make sure that you choose to do a new install, not an upgrade. Then when you are asked to enter a product code select Skip the first time and Later the second time (if I recall correctly). When you are done with the installation you will find that Windows is still activated.
