Well, we've started up a community project on SourceForge.net for adding drivers to ESX/ESXi (see link below). I've got a couple of Wiki pages out there describing how to get things going, and I've checked the code into SVN for the first driver that I ported - the Realtek 8169 Gigabit Ethernet driver. I also have an initial binary download for this driver for anyone who wants to try it out. The download is in the form of a .tgz file that you can add to the boot configuration of your existing ESXi system (see the Wiki for detailed instructions). It has the r8169.o module and an updated simple.map file.
http://www.sourceforge.net/projects/open-vdrivers
http://open-vdrivers.sourceforge.net
