Not sure about the PHP why? Each form is different, however, it's all on the same page with the HTML portion. Each page has different ID's on their textboxes, so which page is selected at that current time shouldn't have a factor really. For example, perhaps the first textbox on the first tab has an ID "sltcountbtn", and the button in the same position on the second tab has an ID "btnsomething". Regardless the PHP takes these values in as input all together and uses them for the submit process. :)
PHP and SQL is pretty simple. This is basically what Laxer does with the DRT, so perhaps he can help you here as well. :) Whenever I do PHP programming, it's usually for creating plugins for my own forum. And sometimes it requires interaction with the MySQL database.