[Touch CDMA General] tatnai:
they may be changing around the .nbh file stuff, so this answer is depending on what happens with that, BUT... you shouldn't need to flash a new .nbh to change your system unless you need to change resolution. if you don't, read on.

NOTE: the process is the same whether running on NAND, or on SD card (ext2 or regular sd). Just don't mess with the boxes at the top of the install menu that say where your sys and data are installed.

TO RUN AN UPDATE that someone has provided in their thread for their build:

1. place the androidupdate.tar in the /andboot folder on your sd card

2. reboot your phone, hold this button until you see the install menu

3. from the bottom portion of that menu, select "Install update". click yes on the popup menu that notifies you that this will adjust the system files.

4. wait. it will eventually finish and kick you back to the install menu

5. go to "quit" and click it.

TO CHANGE FROM ONE ROM TO ANOTHER (same class, i.e. donut to donut)

Note: if you have a data.img, you technically should be able to keep it while moving between ROMs of the same class (i.e. donut rom to a donut rom, or eclair to eclair rom). just make sure to clear the dalvik cache before the new one boots up. however, if there are any problems, the first thing you should then do is wipe your existing data.img using the install menu and the boot your new system allowing it to create a fresh one.

1. place the new ROM file (androidinstall.tgz) into the /andboot folder on the root of your sd card, overwriting any previous install file that was there before

2. reboot your phone, hold this button until you see the install menu

3. from the bottom portion of that menu, select "backup /data", then select "yes" to overwrite old backups (btw, you can rename any databackup.img in the /andboot folder to anything you want to keep multiple backups; when you want to revert to a particular data.img backup, just rename it to databackup.img before going to the install menu). this will give you a backup of your current data just in case something goes wrong. it will take a while to complete, and eventually take you back to the install menu.

4. from the bottom portion of that menu, select "clear dalvik cache". allow this to run, it will return you to the install menu when complete.

5. from the bottom portion of that menu, select "Install system". click "yes" on the popup menu that notifies you that this will overwrite the system files. a second popup will open asking if you want to wipe your /data, select "no" for this to keep your current data file. once it installs, you will be returned to the install menu.

6. select "quit" from the bottom of the menu. this should boot android. first boot after clearing the dalvik cache, installing a new system, or wiping a data.img will take a while, just be patient

TO CHANGE FROM ONE ROM TO ANOTHER (different class, i.e. donut to eclair, or cupcake to donut)

Note: I would not recommend keeping your data.img while switching between different versions of android.

1. place the new ROM file (androidinstall.tgz) into the /andboot folder on the root of your sd card, overwriting any previous install file that was there before

2. reboot your phone, hold down this button until you see the install menu

3. from the bottom portion of that menu, select "backup /data", click ok to overwrite old backups (btw, you can rename any databackup.img in the /andboot folder to anything you want to keep multiple backups; when you want to revert to a particular data.img backup, just rename it to databackup.img before going to the install menu). this will give you a backup of your current data for future use, i.e. if you decide to return back to that version of android. it will take a while to complete, and eventually take you back to the install menu.

4. from the bottom portion of that menu, select "Install system". click "yes" on the popup menu that notifies you that this will overwrite the system files. a second popup will open asking if you want to wipe your /data, select "yes" to delete the current data file. once it installs, you will be returned to the install menu.

6. select "quit" from the bottom of the menu. this should boot android. first boot after clearing the dalvik cache, installing a new system, or wiping a data.img will take a while, just be patient.