A great tool. I just installed a 64-bit Windows OS inside the player and it works. As you can see from the screenshot, the Ferrari 4000 runs Windows XP Professional x64 Edition and is the host. 2 instances of VMware Player run 2 VMs, one is 32-bit, the other 64-bit. Great tool for demos that require more than one 64-bit OS and you have to travel to a customer site. Just take your laptop, install a few VMs and off you go.
How did I install the 64-bit VM in the first place? I downloaded VMware Workstation trial and created an empty Windows guest OS environment. Back in player, booting this environment picked up the XP x64 boot CD in the host drive and that's all. From there it is a standard install.
Of course, a license of VMware Workstation would also do the magic but this is more fun and the player is for free. The Microsoft virtualization products don't support 64-bit guest OSses.