I got a 40Gb (IBM) to upgrade my Pismo that was originally came in a G4 Powerbook that was erased and zeroed out with no OS. When I have the hard drive installed, it does not give me the flashing "?" telling me it cannot find a system folder and freezes when I try to boot from an OS CD (9.1 in this "test" case). I also tested it with the Fujitsu 18GB that I upgraded my WallStreet with and got the same results. My original WallStreet 2Gb gives me the flashing "?". But when I remove the 18 & 40Gb hard drives and reinstall everything, it does what it is supposed to and I can boot from the OS CD. I went to my local Apple store and they told me it appeared I had the drive installed correctly in the caddy. I installed the caddy minus the hard drive and it gave me the flashing "?". I decided to try a 2nd 40Gb (Toshiba) and 2nd hard drive caddy but got the same results. I found out that I am running firmware version 4. 1. 8f5. Could that darn firmware version be the problem? Any thoughts? Thanks in advance for any help!