Connecting Navision using ADO SQL Query Parameter.

I am trying to connect the local client to SQL Server database using the ADO functionality. It is working proper. But my question is that how can i like a parameter to the query.

nm :='JOHN';
SQLString := ' SELECT * FROM [MSRETAIL].[dbo].[MS Retail$CUSTOMER] ' +
' WHERE [NAME] = ' + nm ;

I have declared the nm as a text parameter in global variables.

When i run the code it gives me error 'invalid column name JOHN';

How to link the parameters to the query.