If I'm not mistaken, ATI is rebadging the 8500 as 9100 since the 9000, 9500 and 9700 came out so they are basically the same card. They also did this with the original Radeon when the 7500 and 8500 came out and it was renamed 7200. This is because the 8500 is a faster card than the 9000 which is cheaper. With a lower model number people would think it's slower and not buy it.
I think, all your doing with this flash is putting the latest BIOS on the card (not necessarily a bad thing) but I would definately recommend backing up your old BIOS before doing it and unloading the Radeon driver in Windows then reinstalling it after flashing it. As always, when flashing a graphics card, it's not a bad idea to have an old PCI card handy should something go wrong. You can then at least get a display up and reflash the Radeon.
