Vmware Server is probably the most basic Vmware solution for virtualization - thanks God it is still free software. How to move your virtual machine from Vmware Server 2.0 to ESXi?

Simple but long... Get the other free tool from Vmware - vMware vCenter Converter Standalone. Just a converter - nice and straightforward tool. And convert your existing virtual machine to ESXi one. It might be a long process.

Vmware Server 2.0 > vMware vCenter Converter Standalone 5.0 > ESXi 5.0

I might experience problems with older versions of the converter - so for ESXi 5.0 get the newest converter.