The program, once running, can run NT, Linux, and Windows 9x. Although VMware is interested in supporting as many x86 OSes as possible, they say that they have no plans to support the BeOS right now.
Stability is also quite impressive, especially for a beta product.
So far, I've used the VMWare beta to run RedHat Linux 5.2 from within NT 4 SP5. But there's a little bit of coolness I want to share with y'all. See, when I was reading up on this product, I noticed an interesting little bit of information. You see, at work, I primarily use NT, but I need easy access to Linux so I can check things out quickly. Red Hat was working with only one minor hitch.