It's really pretty simple. The ROM will be a file that you download that is called something.zip (such as kaosfroyo-v31.zip). Basically, you do this:
- mount the SD card to your computer. You can do this from the phone, connected via USB cable. When you connect and choose to mount the phone to the PC, it will open a drive called "NO_NAME" on your computer. Copy the ROM file to the top directory of your SD card (i.e., the NO_NAME removable drive.) MAKE SURE THAT IT IS IN THE TOP, OR ROOT, DIRECTORY OF THE SD CARD. DO NOT PUT IT IN A FOLDER ON THE SD CARD. After the copy is done, eject the drive from your computer; when you get a message that this is complete, you can turn off the data connection to your PC from the notification on your phone. Power off the phone.
- Hold down the Vol-Up key and press the power button. When you see that the phone is starting, you can release the power button, but you should probably hold the Vol Up button until the Recovery menu starts.
- Use the trackball to move within the Recovery. Go down to the Backup/Restore and press the trackball. Press the trackball on Nand backup. Press the trackball to confirm.
- When that is done, it will return to the Backup/Restore menu. Press Vol-Dn to go back up to the main menu.
- Trackball down to the wipe menu and press. Go down to Wipe Dalvik cache, and press the trackball. When that is done, press the trackball to Wipe data/factory reset. When that is done, press Vol Dn to go back up the main menu.
- Trackball down to Flash zip from sdcard and press trackball. Trackball down to the ROM that you want to flash. When it is done, I believe it returns you to the main menu. Press trackball on Reboot system now.
That should be it ...