Yes,
Check the thread for Custom Themes for OS 4.1
http://www.blackberryforums.com/showthread.php?t=30280
there are a lot of theme in this thread start your seach on the last page and work backward. some the earlies themes are no longer available at the original links, but if you want one that the link does not work just ask someone will relist it.
You can use only themes that were designed for the 7200 or 7500 series with your phone