Thanks for your response! I actually was trying to use the pre-installed NIC that was using an unsupported Intel Chipset (82567-LM3) for ESX 3.4 Update 4. I had to use that old version of the software for the Offline Desktop feature in VMWare View 4.0.
Fortunately, I was able to get ESXi 3.5 Update 4 to work! I used the instructions here http://vm-help.com/esx/esx3i/customize_oem_tgz.php
to create a custom ESXi install disc with ISO Master; the instructions here worked perfectly and I was able to set up my demo.
I wasn't ever able to get ESX 3.5U4 to work, and I am still curious to know if any one out there knows how to slipstream RPMs into the disc (ESX is built on Red Hat Linux and does use RPMs. I was able to locate the folders with all of the .rpm drivers but I couldn't figure out how to edit the text files that indexed all of them and loaded them). If anyone figures that out, I'd love to hear about it.