Found this on the internets.
There were a couple of variants on the plist file method in the original hint. Below is the one that worked for me. Other variants failed or gave me problems, but the below has been happily doing its job since 10.3.0 all the way up to the present.
(The followng pasted in a file called autodiskmount.plist in my /Library/Preferences/SystemConfiguration folder.)
<?xml version=”1.0″ encoding=”UTF-8″?>
<!DOCTYPE plist PUBLIC “-//Apple Computer//DTD PLIST 1.0//EN” “http://www.apple.com/DTDs/PropertyList-1.0.dtd”>
<plist version=”1.0″>
<dict>
<key>AutomountDisksWithoutUserLogin</key>
<true/>
</dict>
</plist>