Let me give you a little more. ODBC uses a "DSN" to identify the data resource to be connected to. This can be a name stored in the ODBC configuration or it can be a full ODBC connect string. There should be a line in your code that looks like this:

$db = new Win32::ODBC("someDSN");
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or

$db = new Win32::ODBC("Driver={SQLServer};Server=Your_Server_Name;Data
+base=Your_Database_Name;Uid=Your_Username;Pwd=Your_Password;");
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And that you should check for success as well. If that call doesn't work, your $db reference won't be useful for anything.