Mac OS X v10.5.8
pgAdmin v1.10.2
1. Open Query Tool
2. select Graphical Query Builder
3. drag one table onto canvas, select a column or 2
4. drag another table onto canvas, select a column or 2
5. drag a join link between the tables
6. Click the Join tab at the bottom portion of the dialog
7. Alternate mouse click the join line on the canvas and select Delete Join
8. wait..., keep waiting... poof!