Just a heads up, you can now get a ISBN column. re:
http://www.google.com/url?sa=t&sourc...CYiNSs4uMB6YHA at bottom
or: Assuming you are running 0.7.21 [or newer], create a custom column of type 'column built from other columns'. Then enter as the template '{isbn}' (no quotes.) See the tutorials section of the manual for more discussion of what you can do with templates.