I’ve found a couple of ways of doing this with Ubuntu, the quickest way is to make use of the isohybrid tool from the syslinux project.

Download the latest version of the ESXi 5.0 install iso, and then use the following command in a terminal to convert the VMware install CD to a hybrid CD:

isohybrid VMware-VMvisor-Installer-5.0.0.iso

Then write the converted image onto a memory stick just as would a normal disk image with dd by using this command in a terminal:

sudo dd if=VMware-VMvisor-Installer-5.0.0.iso of=/dev/sdX bs=1M

There is also a way to unpack the ISO onto a memory stick and make it bootable, but it’s a little bit more long winded.