Blackberry theme problem. COD file?

I downloaded a few themes for my blackberry curve 8310 that I unzipped and theres only a few COD files and one JAD or JAR i forgot in each folder. and then I opened my desktop manager. They only allow alx. files. What is a COD file and what am I supposed to do in order for me to get the theme onto my blackberry??? I'm so confused, please help. Thanks!