If you were using a flash drive or external hard drive to install VMWare ESXi then you will notice that when you want to use that drive for something else, it only appears to Windows as ~4Mb.
You will probably try to format it inside of Windows but this will still only leave you with the 4Mb of usable space as if the max capacity of the drive has been reduced. Even in Windows Disk Management, you will be completely unable to remove the partitions that were created by ESXi
In order to return this drive to its original capacity you must use the HP USB Disk Storage Format Tool. Just format it with this program and then you will be all set.
For anyone out there who may have the same motherboard as I do, the ASUS A8n-SLI Deluxe Socket 939, I wanted to let you know that it DOES in fact work with VMWare ESXi. Since their hardware compatibility list (HCL) is limited to commercial off-the-shelf servers I wanted to note that it is fully functional (except for that only 1 of the 2 NICs work).
I was able to attach a storage pool directly to the onboard SATA controller and 1 of the 2 gigabit NICs is supported by ESXi with no modifications necessary.
I was also able to plug in a USB drive with ESXi installed and boot right into the OS, connect remotely, and manage the server.
Next I wanted to try to set up VMWare ESXi. I also read about how you can run ESXi off of a flash drive and I thought I would give this a try so I could dedicate the entire physical hard drive to running WHS.
I read that I could run through the installation normally and just tell it the installation destination is the USB stick, however this did not work for me as it said it was unable to find a location to install to. And after loading the installation files I was forced to restart and try again.
I did find these great instructions that guided me through the process in a lot less time then it would have taken to run through the standard installation. I used Method #2 with WinImage and the whole thing took under 10 minutes.
I stuck the USB stick into the PC and it booted right into ESXi, obtained an IP address, and I was able to download/install the VI Client to manage the server very easily. The VI Client is very overwhelming at first but once you understand its layout it becomes manageable.