It is possible to copy Esxi 5.0 installation cd content to USB pendrive in order to install Esxi 5.0. Also you can boot from this pendrive and install ESXi 5.0 on it.
Prepareation in windows OS:
First format USB drive with FAT 32.
Make this USB drive bootable using *syslinux.exe version 3.86
Usage: If USB drive letter is E;
syslinux.exe -a -m E:
After copy process rename file named isolinux.cfg to syslinux.cfg and edit the file using text editor.
Find line APPEND -c boot.cfg and change to APPEND -c boot.cfg -p 1