Just succesfully flashed a 78 and a 79 in Vista32 with Via 6421
Followed the JF manual closely but not completely.
Fresh vista 32 install (as I use 64 bit)
.NET Framework 3.5 SP1 and updates all installed
Installed portIO 32 manually
Installed viamraid.sys manually after port I/O installed (could not dump firmware useing port I/O commands in JF)
Opened JF set Mode B, did the drive door open, unplug, wait, plug back in and close drive door on 78 Mode B set
For 79 had to use the unlock CD
Waited for windows to pick up drive, then refreshed list and drive was there
Then switched from Port I/O mode to Win Api mode and dumped the drive, once dumped saved to the firmware folder as specified in JF README
Got all my drive info so I knew which firmware to add to that folder, both the original version, and the iXtreme version, as my drive had 1.4 on it
Then restored the firmware as asked to set up the flash, and saved the original to a different location.
Then clicked flash iXtreme, waited for it to complete, and then shut down PC, unplugged drive, and all was good when re-installed to the XBOX
Good luck all, hope this helps some of you.