How create a virtual network for practice?

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http://serverfault.com – I need to organize a virtual network for practice with Windows Server 2008 and several workstations with Windows OS. To make it all I only have a laptop with Dual-Core 2.10Ghz, 3 GB RAM, 50 GB free space and Windows 7 on it. Also I have external USB 3.0 hard-drive with 250GB free space and flash disk with 8GB space. What can you suggest? Because I have limited resources, I think to install ESXi 5.1 on the main disk of my laptop as second OS, with installed Windows 7. I have no idea will it work or not, but after that I want to try to create hosts using availible space on external hard-drive (HowTos)