I have read that this is not possible on a Mac, as eSATA requires a driver to load on current hardware. I bought an Apiotek single port pc express card for about £12 in p&p on eBay, only to realise that this was not supported on OS X. Or so I thought. I put my old MB hard drive in a no-name SATA enclosure and attached it to the pc express card in my MBP SR. For good measure I installed the driver direct from the chip manufacturer (Silicon Image) for the pc express card with 2 ports which is Mac compatible, figuring that I could easily remove it if it did not work. I rebooted and held down the option key. Lo and behold, the MB hard drive installation appeared as a bootable option so I selected it. It got to the swirling pattern before I got a kernel panic, which I put down to incompatibility between the MB and MBP hardware kexts. The main thing is that despite reports it does appear that booting from external eSATA is possible with current hardware. Under Tiger 10.4.10, I could access all the files on the external SATA drive which appeared in Finder with a generic internal HD icon. The card is a bit flakey in that I cannot eject it once inserted, even if I power the card down as it leads to a kernel panic. However it is fine if I leave it in and does not seem to affect performance otherwise. I tried the card in a friend's MBP with Leopard installed, and the card ejects without kernel panics, no driver installed. Moreover, although the card itself is not recognised, full details appear in the System Profiler. Anyone else tried any other cards, which work more gracefully, and how did you get on?