Needed to install VMware ESXi from a bootable USB key as the HP server I’m working on has no optical media drive and the virtual media applet in HP iLO 2 disconnects the media (either CD or ISO) part way through.

Tried using UNetBootin, which worked to create a bootable USB but for some reason could not boot to the installer. Tried a bunch of different options at boot: but couldn’t get it to work.

Fortunately, Internet to the rescue: VMware ESXi – install from USB thumb drive

Extracted the ESXi ISO onto a formatted (FAT32) USB key (I used 4GB key) using WinRAR. Downloaded syslinux 3.82 and used it to create ldlinux.sys, changed ISOLINUX.CFG to SYSLINUX.CFG for the bootloader to find it, booted the server with the USB key – boots straight to ThinESX.