I'm currently building a signup form and I find myself resorting to tables in order to align things properly e.g. the MySpace equivalent where I would use a colspan to achieve the even spacing between the three birthday text areas and the other text inputs. Is this going against conventions and should I be looking into more advanced CSS?
I think you should drop the table all together and use more CSS. You could look into this: http://www.webcredible.co.uk/user-friendly-resources/css/css-forms.shtml