There have been a few threads about how to move a time machine backup to a new disk and maintain the existing backups. Some have done this with carbon copy cloner. This also works with the built in disk utility in Leopard. I turned off time machine first. Then I booted with the Leopard install DVD and ran disk utility. I partitioned the new disk and gave it the same name as the old time machine drive (not sure if that's necessary). I then used the restore function to clone the old time machine disk to the new one. I rebooted, turned time machine back on and it picked up where it left off. The first backup with the new drive took a little longer than expected considering nothing had really changed but all the prior backup data is intact as if nothing had changed.