Already connected to the database

[sutterp]

I need to do some pre-processing in my program. This pre-processing connects to the database via an include file and returns the MySQL link identifier as a global variable.

[mark]

Reusing such native database connections isn't possible in Structures_DataGrid. This would require that we have special code for every of the databases that PHP supports.

You didn't write it, but it seems that you want to use a SQL query in the bind() call. This works only in conjunction with PDO (not available on PHP 4) or the PEAR packages DB (deprecated) and MDB2. For MDB2 you'll find some details here:
http://pear.php.net/manual/en/package.structures.structures-datagrid.structures-datagrid-datasource.mdb2.php

If you have further questions on this, don't hesitate to ask.