Howto: Prevent Future OTA Updates on Your Android G1

First Get r00t
Then Follow these directions
mount -o remount,rw -t yaffs2 /dev/block/mtdblock3 /system
Then move the otakeys.zip file which prevents the update:
mv /system/etc/security/otacerts.zip /system/etc/security/otacerts.zip.nothankyou
That one line will move the otakeys to a location the updater can't
check for it - and once the OTA update is downloaded, it will be unable
to apply.