VMare vSphere Hypervisor (ESXi) is a free fully functional hypervisor that lets you virtualize your servers and run your applications in virtual machines. More info at http://www.vmware.com/products/vsphere-hypervisor/overview.html and documentation at http://pubs.vmware.com/vsphere-50/index.jsp
This blog is about creating a bootable Installer of ESXi that you can use to install on a computer. If you wish to install ESXi directly on USB thumb stick and boot from that then check out one of the following
At the time of this blog version 5.0 of ESXI was available and I created this on a Apple Mac running Operating system 10.7.
For a hardware compatibility guide check out http://www.vmware.com/resources/compatibility/search.php?action=base&deviceCategory=server
At the time of writing this the Apple servers running the Xeon 55xx processors are officially supported. Seems to be strong rumors that the new mac mini's will be officially supported with version 5.1 of esxi. Uu-officially it seems the i5 and i7 and Core 2 Duo apple hardware also seems to be working. There are some issues with old apple hardware with usb keyboard and mouse drivers. For the new mac mini you will need a custom Ethernet driver.
There is a nice write up installing this on a Apple Mac mini using a custom Ethernet driver at http://paraguin.com/2012/01/10/the-mac-mini-vmware-esxi-5-server-part-2-installation/
Steps to create a Standard USB thumb stick ESXi Installer
Step 1 : Insert a USB thumb stick you want to use as your installer disk. You will loose ALL data on this USB thumb stick and it does not have to be very large 500MB will be fine.
Step 2: Download the installer http://www.vmware.com/go/get-free-esxi.
At the time of this blog the file I downloaded was called VMware-VMvisor-Installer-5.0.0.update01-623860.x86_64
Step 3 : Download UNetbootin from http://unetbootin.sourceforge.net. This is a great app that is available for Apple Mac, Windows and Linux and will save you lots of time
Step 4 : Launch the UNetbootin application downloaded in Step 3. Select Diskimage (ISO) and select your .iso file you downloaded in Step 2.
Step 4 : Choose type of USB Drive and select the USB thumb stick you inserted in Step 1
Step 5: Click OK and watch the bar move across your screen for a few minutes
That's it you are done. On some hardware platforms that you want to boot from a USB thumb stick you may need to modify the BIOS to boot from USB, this is refereed to as "UEFI" on some systems.
Note : if you get a message "override menu.c32" when running this then at the error prompt select no and it will drop into the shell "boot=" prompt. From here type "mboot" and it will work