The problem is a bit more complicated than that. My SR MBP came with Tiger as the installed OS but i upgraded to leopard. i have an imac that also came with tiger and eventually i upgraded it to leopard. I installed tiger on an external drive to run Avid MC and i intended to run on both macs. I used the MBP to install Tiger on the external drive, i then booted from the external drive in the iMac. It ran fine and i installed some updates including the iMac software update. However, now when i hook to the MBP and try to boot form the external drive, i pass the apple logo and then it takes forever at a greyish blue screen. It wont let me in. It boots fine in the iMac. Anyone familiar with the problem? is it due to changes in resolutions? 1440x900 vs 1920x1200? is it the imac software update? thanks for reading.