[Zope] External Methods

[JB]

Please excuse my lack of zoping intuition but I hoped someone could help
with this problem. I read all the doc's I could find but seem to be
missing something. It goes like this...
I have a ZSQLMethod that returns some tuples. There is a field in the
tuple which I wish to use to lookup an external file and return a jpeg,
if available.
I've created an external method called 'getPic' which I wish to pass the
key field to locate the file with but I can't seem to get at the
variable.
e.g
----------
<!--#in sequence -->
  <td><!--#var pic_key null=""--></td>
  <td><!--#var "getPic( <!--#var pic_key --> )" --></td>
<!--#/in -->
----------

This doesn't work for reasons not obvious to me.

I've tried creating a class to handle the records. No go.
Basically, the External method can't get at the vars defined on each
loop thru the sequence returnd from the SQLMethod.

Any insight would be appreciated.

thanks
jb