VMware ESXi is a full fledged bare-metal hypervisor that fits into a 32MB footprint. VMware ESXi is essentially VMware ESX without the server console.
You can run virtual machines created by Microsoft Virtual Server, Microsoft Virtual PC 7 or greater, VMware Server on VMware ESXi by using the free VMware Converterto import virtual machines. VMware Converter also supports conversions from sources such as physical machines and certain 3rd party disk image formats.
Virtualizing servers is not a trend, but the future of the datacenter. If you’re still maintaining all physical servers, now is the time to give virtualization solutions consideration.