Download the update from here: https://android.clients.google.com/updates/signed-kila-ota-115247-prereq.TC4-RC19+RC28.zip
Note that the filename has RC28, but it actually updates to RC29.
Make sure your phone is fully charged and not connected to your usb charger or cable!
Follow the directions exactly and relax, this will not damage your G1
1. Copy the zip file to your root sd card folder after renaming it to update.zip
2. Insert the sdcard to phone and press the home key and red off/on key at the same time(hold it in)
3. when you see a triangle and small cellular picture open the keyboard and press (alt+L)
4. You will then see yellow text, press (alt+S) check what will do in the text.
5. When you finish press home +back to reboot and wait. for the flash of radio
6. you will see chip picture with arrow..wait,wait AND THE PHONE REBOOT ITSELF.
Your finished, wait until your G1 reboots 2-3 times and it will be finished!