ESXi - Install from USB and To a USB

Install from USB

Instructions
Format USB drive as FAT32.
Download Syslinux. http://www.kernel.org/pub/linux/utils/boot/syslinux/
Run win32/syslinux -f -m -a usbdriveletter: or win64/syslinux64 -f -m -a usbdriveletter:
Copy contents of ESXi ISO to USB drive.
Rename isolinux.bin and isolinux.cfg to syslinux.bin and syslinux.cfg
Create file on USB drive called ks.cfg. A simple one is listed below. For more information on this see pg. 36 of the documentation here: http://www.vmware.com/pdf/vsphere4/r41/vsp_41_esxi_i_vc_setup_guide.pdf
start ks.cfg
vmaccepteula
rootpw password
autopart --firstdisk --overwritevmfs
install usb
network --device=vmnic0 --bootproto=dhcp
end ks.cfg
Edit syslinux.cfg - under the ESXi Installer line, add "ks=usb" after vmkboot.gz in the "append" line, like so:
append vmkboot.gz ks=usb --- vmkernel.gz --- sys.vgz --- cim.vgz --- ienviron.vgz --- install.vgz
You need to do these two things if you downloaded the latest version of Syslinux, something past version 4. Otherwise you will get an error to the effect of "not a valid com32 image" or something when you try to boot.
Copy %syslinux%/com32/mboot/mboot.c32 to USB drive (overwrite)
Copy %syslinux%/com32/menu/menu.c32 to USB drive (overwrite)

Install to USB
http://www.techhead.co.uk/installing-vmware-esxi-4-0-on-a-usb-memory-stick-the-official-way