I recently needed to install Ubuntu Linux on a Server with no CDROM to an IDE Disk On Module. For those of you that don't know a Disk On Module or DOM, is a flash drive that has either an IDE or SATA interface so it looks just like any other hard drive to your system.
After trying many different scenario's I found the Ultimate Deployment Appliance. http://www.ultimatedeployment.org/.
I simply downloaded the Virtual Machine to my ESXi server, ran the configuration and pointed the Ultimate Deployment Appliance (UDA) to my Ubuntu ISO. When I powered on the server, the Network Interface Cards PXE environment found the UDA and presented me with the option to boot to the Ubuntu install CD.
The installation worked like a charm.
Best of all, you can use UDA to install ESXi via PXE.
Check out RTFM-ED, http://www.rtfm-ed.co.uk/vmware-content/ultimate-da/, for more information and some quick start guides