Head down into virtualization

For my new server, I want

• split the functions into dedicated firewall/router, file server and UNIX development environments
  
• I also would like to have a central user directory for my 4 active users and numerous personal and lab machines
• Of course, I don't want extra boxes raising my electrical bills

So, it's time for virtualization, no doubt. And, if I could virtualize my lab, which I need only sporadically, how great it would be!

Looks like there are VmWare ESX, MS Hypervisor and Xen around which I could use to host my new setup.
I don't know much about Xen, but I feel it's not really of mainstream commercial quality. This should not be a problem for a person fiddling with UNIX for fun, but I want at least the foundation of my new building to be stable.
MS Hypervisor seems to have very good hardware support, as it runs under Windows essentially. But it's very far from being free. And, I don't know how much it loves UNIX guests. I generally feel it is not kosher to bring this thing home.
I had previous experience with VmWare products and they did work. It wasn't fun running virtual machines on my work laptop, but this time I will have a separate rig for this. So let's look at VmWare ESXi first. It is given for free, has a sizable user community but is picky about the hardware.