Dr.Acrobat (no adobe), Two partitions would permit you to run ESXi or Windows, but not both at the same time. I assume your second one would be windows, since that is what vSphere client runs on.
Best option for home lab: get a cheap computer or laptop to be your ESXi host and install ESXi on it; use another machine for administration. This setup is a microcosm of what a datacenter looks like. You have a bunch of servers running ESXi and you manage them all from another machine. You can even get a Ethernet switch and get another cheap computer or laptop and have multiple ESXi hosts in your "home DC".
Best option for moveable virtual environment: Use a "normal OS". Use Windows, OSX, some flavor of linux, then install a type 2 hypervisor on it. VMWare workstation and fusion both work well. If you are on a linux host don't be afraid to tap into KVM, because you shouldn't be dogmatically attached to VMWare products. For simple testing VirtualBox isn't bad either.
Worst idea: partition laptop hard drive between ESXi and Windows. Why? Because you'll never get to run them at the same time, and isn't that the whole point?
-gns