You can manually SSH into the iphone and add the themes to the Summerboard themes directory and they will show up in Summerboard. This will also allow you to use ALOT more themes, as most of them are not on installer.
Search for tutorials on using SSH on your phone and installing the Summerboard themes, there are many on this board.
As for the Roms, you must also SSH into your phone and place the roms in a certain directory. There are guides at
www.zodttd.com to tell you where to place them.
To find roms......Google it. We cant post sources for that stuff on this site.