I have done a lot of work on this and determined that the Book drive is not hot swappable but...
..Start drive, wait for lights to stop flashing. Plug into system and power up system. System hangs after windows progress bar. Unplug eSata cable, windows continues, but no drive installed.
..As above but don't plug into system until the round windows logo appears. Windows loads OK, the drive is recognised in 'Computer' and 'Management' and is accessible sometimes (maybe timing of plug in). All OK.
..As above but sometimes opening 'computer' hangs. Unplug drive cable and a message that the drive needs formatting.
Whenever the computer hangs it is usually releasable by unplugging the eSata cable. Plugging back in sometimes works?
..the drive goes busy and windows is waiting for something, removing the cable provides that by removing a busy signal?? Odd that windows is released rather than crashing, which indicates that windows requires some feedback.
..the format on the drive is somehow supposed to be different. I notice that using windows format leaves an empty drive, using Acronis format gave two system folders (or left them but did a 'quick' format).
Final conclusion, it is not the eSata on the Acer. It is not the cable or sockets. It could be the WD Book drive remaining busy. It could be something in Vista 64 but not likely, others had the problem with XP.
Drivers. I got the latest drivers for NVidia GeForce 7100/nForce 630i v15.26 16 March 2009 for Vista 64. Installed, all appeared to be OK but the drivers shown in windows are still the microsoft ones 2008. Anybody can help with that?