With close to 10,000 views, this video has finally been superceeded by the release from Sony of Version 1.2 of the firmware for the EX1. You can watch that video here vimeo.com/10106072.
A demonstration of a Sony PMW-EX1 being upgraded to firmware 1.11 which allows it to function with KxS and other XxS alternative media solutions.
Don't forget to replace the maint. port cover after you have finished.
There are also some pdf files in the firmware package with instructions and error codes. Use and read them as nessesary. Some of the comments below are important to read too.
You'll have to figure out installing the driver for the maint. port using the indicated inf, I didn't get time to add this part.
I have also been told you can do it on a Mac with virtualization software: "I just did my EX1 on my MacBook Pro running Parallels 4 with XP. The key is to select "connect USB to virtual machine" when you connect the USB port AND to check to little checkbox to keep it that way so that when the installer reboots, the USAB port does NT disconnect." I'll leave you Mac guys to understand all that ;-) Be warned, at least one person has bricked their EX1 doing it this way though, I personally recommend a PC or at least a MAC under a bootcamp boot.
I upgraded my own EX1 some time ago (the EX1 in this video was not mine). I recently put it in for a service under warranty (battery drain issue etc) and had no problem with getting warranty. Funnily enough they claimed they upgraded the firmware but it still came back with 1.11 (I didn't argue with them about that, I just let it slide as I now have on paper an official upgrade for it).
This is a very quick draft edit but has most of the content needed.
Other XDCAMEX information at http://www.xdcamexinfo.com