Thanks Joe, that pointed me in the right direction. For anyone else looking to do this here's what I did to make the checkbox list flow horizontally. The list renders as UL instead of table.
As Joe pointed out add this to the theme.skin in your current skin. The SkinID is the part I didn't catch at first and needed so it applies to the FormWizard module. Touch the web.config so the change takes effect.
<asp:CheckBoxList runat="server" SkinID="FormWizard" RepeatLayout="unorderedlist"/>
I then gave my form a custom CSS class called "QuoteForm" in this case. Then add some CSS to your stylesheet like below and you'll have a horizontal checkbox or radio button list.
.QuoteForm ul { list-style: none; }
.QuoteForm li { display:block; float:left; margin-left:8px; }
JOE: I wonder if the default behavior of the checkbox list should render as a UL instead of table? It seems more flexible and users wouldn't have to modify the theme.skin file? I suppose you could even get really fancy someday and offer a setting with checkbox/radio lists for "layout direction".