If you go under START -> Settings there is an icon marked Today. From here you can change your theme, but there is a tab at the bottom called ITEMS.
From here you can move items up and down and you can uncheck some of them that display.
If you are just not happy with the default Today screen, check into Pocket Breeze at
www.sbsh.net. I love this program it reorganizes your information into something so much better.
Hope this helps.