Here is a good reference for constructing web forms. It succinctly defines the pluses and minuses for different layouts.... There just is not much in the way of choice for web forms.

http://www.lukew.com/resources/articles/web_forms.html

The full article:
http://www.lukew.com/ff/entry.asp?144

Nice layouts:
http://www.lukew.com/portfolio/web_applications.asp

and another reference:
http://www.rosenfeldmedia.com/books/webforms/