I just installed SQL Power Wabit on a Windows 7 64 bit machine without incident and connected to a SQL Server 2008 DB without any trouble.
However, in creating my first query, none of the columns I select from the table display in the playpen when I drag them there. The Constants box is there, but nothing else. I can even drag a column name to the Where text box, but can't drop anything into the playpen.
Just to clarify, have you tried dropping a whole table in the playpen, or just the individual columns? Wabit's query editor takes entire tables, then lets you select/deselect columns afterward.