My Xecutor 2.6 modchip came with a legal Cromwell BIOS pre-installed which is good enough to boot the Xbox but has no other features apart from it's own setup screen to enable flashing. However I was supplied with the URL of where to download the BIOS you need to enable the full features of the chip. Once I had this BIOS file I needed to flash the chip, and this initially proved problematical.
At first I tried to make a boot CD with the BIOS on but for reasons I won't bore you with this proved to be a dead end (basically I found instructions for using a PC app called Qwix to make an xiso disk image but this kept crashing XP under Virtual PC). Then I noticed that you can flash the chip over a network from a web browser! This was really easy - you just boot the Xbox and when the modchip displays it's setup menu, it also displays it's IP address (I'm assuming your Xbox is already connected to your network via a hub or crossover ethernet cable). So I fired up Safari (I'm sure other browsers like Firefox and Camino will work just as well) and entered this IP address. A simple front-end appears where you select your BIOS file and click upload. The BIOS then flashes and your Xbox shuts down. Job done!

cromwell

The site I bought it from doesn't mention you have to flash the BIOS in the product description, but many of the people leaving comments about this product mentioned it so I knew it was something I'd have to do. I'm just glad that the network option worked as working out what type of media your Xbox will read, and then trying to create the disk in the necessary xiso format was rather tricky, even with Virtual PC to hand.