Aftrer trying unsuccessfully to upgrade to 3.5 in Vista (several errors, no matter what I tried) I stumbled onto a solution I thought I would share. Steps:

1. Get the upgrade you want
2. Get The latest stock upgrade from sprint, ver, etc
3. set your computer to view hidden files
4. go to c:\JoeUser\AppData\Local\Temp and set it to list files by date
5. Double click on the STOCK exe file. Leave the installer program alone. Do not continue yet.
6. You will see a new folder in temp. Open it.
7. Open the upgrade exe with winrar
8. Copy the .nbf file from the upgrade folder to the temp folder
9. Continue the installer program.
10. When I reboot, I reboot again before 3 seconds so I do not get the spring junk.

Some let me know if I am off track, but it worked great for me.

Can you help me out with these steps.

5. Double click on the STOCK exe file. Leave the installer program alone. Do not continue yet. (didn't see this file) If you mean the file I just downloaded I used Col3.3beta3SprintNoJunk

6. You will see a new folder in temp. Open it. (see a new folder RarSFX0)
7. Open the upgrade exe with winrar ( didn't see this file)
8. Copy the .nbf file from the upgrade folder to the temp folder

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Sprint PPC 6600 --> 6700 --> 6800 --> 6900 -->?

there is another method that involves changing up the USB driver... i can't recall where a buddy of mine stumbled upon it though.

5. Double click on the STOCK exe file. Leave the installer program alone. Do not continue yet. (didn't see this file) If you mean the file I just downloaded I used Col3.3beta3SprintNoJunk

The STOCK file would be the one downloaded from sprint, not one of the updated ones as the installer built in to them works in VISTA

6. You will see a new folder in temp. Open it. (see a new folder RarSFX0)
Make sure you can see hidden files. It will be the newest folder, if you view by date modified.
7. Open the upgrade exe with winrar ( didn't see this file)
This is the file you downloaded for the 3.5
8. Copy the .nbf file from the upgrade folder to the temp folder