There is a complete list in GP itself which lists all the tables and the fields on each table. But a lot of additional info is not filled out unfortunately. Go to Tools>Resource Descriptions>Tables, then choose the series of tables you wish to view (Financial, Sales, etc.) You can print at this level - so that you see all the tables in the Sales series for example - and you can also go into each table at print at that level - where each field is listed.
Hope that helps.
-Caro