I thought I knew what your problem was, because I thought F9 was the latest (It was 2 weeks ago)! But I just checked GB's website and discovered that F10 is now the latest. Funny, just 2 weeks ago, GB told me this mobo will not be able to use the XP2400 or 2600, but this bios is supposed to support the new chips. We will see...
I updated my bios the same way you did, using GB's USA download site. Mine loaded without any checksum errors (I used a cable modem, so if you had a dial-up connection, that may explain the error).
I updated the bios from F9 to F10, rebooted, but WinXP hung with the splash screen. After I loaded the default bios settings, XP started fine.
Since you have the dual bios mobo, you can always go back to F8, then try flashing it again. F10 works just fine for me!
I don't have access to the manual at this time, and I can't remember how to do it. But your situation is the reason GB uses the "dual bios" design. If the bios gets corrupted by a virus or a bad flash, you should be able to get to the backup copy on the other chip.
If you download the manual from their website, the procedure should be in there.