I agree with Ice that you should switch to the 2025A.
I've read his comments before about the 3 step process though, and I'm not sure what is being referred to there, but more on that below.
Re using USB, I think that there is a high probability that this will not work if you have earlier firmware versions. What often happens is that the 8100 won't recognize the file you have on the USB thumbdrive, often even if it's the same one you have on there. Also, just in case something goes wrong, I would recommend being prepared to use the serial port method.
One other thing, and this MAY only be an issue if you are trying to wipe the receiver clean of hacker firmware ( the "F" versions are pirate, and the "A" versions are factory), but I have always loaded a Clear_sw(HD).bin file, prior to loading new firmware. This shouldn't be necessary after you get to one of the newer firmware versions, and if you use the clear file, then the USB method will definately not work. I don't think however that it is necessary when going from factory to factory, but if anything goes wrong, I'd recommend doing this, so you should have this file handy.
Re three step process, I don't understand. What I have always done with the 8100 is just download the CSUpgrade v3.01.exe program, and run that directly. It may be that certain versions of Windows are lacking some DLL files or something, but with my Win2000 and Windows XP home, the loader worked fine without any step one and step two, whatever they were.
Run this program, and turn off the receiver with the switch. In the program select the file that you're going to download to the receiver, and tell it to start, then turn on the receiver, and everything should go on it's own. There will be progress indicators both on the receiver and the program. Anyway, it's a simple process. I can't go into any more detail right now, because the computer that I have all that stuff on died this morning, and it's going to take me a while to get it back up, so I can't check my notes right now, until I reload the OS.
I do remember reading some instructions about how to do the serial download, which made it sound like there was some timing involved, ie like you had to turn on the receiver, and quickly hit start, or visa versa. That definately was NOT necessary. Once you hit start, you can take your time turning the receiver on. The computer program waits for the receiver to come on.
If the receiver just boots up, then it probably means that you have the wrong cable.