Have you ever tried installing ESXi on a hardware box that is not explicitly supported by VMware? If you try this you will often run into the problem that the original VMware install ISO does not include a driver for the storage controller or network card that is in your box.
There is a community that works on building drivers for such devices (so called Whitebox hardware, see www.vm-help-com), and there are instructions and scripts available for adding these drivers to the original install ISO. However, they all require some (at least basic) Linux knowledge and access to a Linux system.
This has changed now ... I have written a script that automates this task and runs entirely on Windows 7. Visit the project page on this blog site to learn more!