have you read this:
http://forum.ppcgeeks.com/showthread.php?t=5091
for your today screen, you can customize it to your liking by going to: start > settings > today
you can choose your theme (you can download your own themes, they will be in a .tsk file..)
for themes, go here:
http://forum.ppcgeeks.com/forumdisplay.php?f=31
then on the bottom, you can decide what you want to show on your today screen by clicking items..
if you wish to add programs, well, you will have to read about that, theres really no way around it..
for programs that will install on your phone, they will come in the form of a .cab file
for progams that you need to be connected to your pc with, they will come in the form of a .msi or .exe