Form Designer -- customizing layout
Using Jamroom
Not using Form Designer.
The easiest way I have found is to override /modules/jrCore/templates/form_field_elements.tpl and simply add a class name to the table rows (there are two).
Then move the table rows around using jquery. You would wnat to keep the same table structure etc (you dont have to but it keeps things simple), but that allows you to have multiple tables, some side by side, some stacked etc.
If that doesn't provide enough flexibility you need to get more detailed with the jquery, or override all of the form field elements to remove the tables.
If you only need that on one or two forms, override the core templates and add if statements so that the core structure is used on all forms except $_post._uri = "/my/custom/form/uri"