I just downloaded a theme from this site. But I have no idea what to do after I download it on to my computer.

I have already jailbreaked my ipod and I have installed BSD Subsystem, Installer, OpenSSH, Community Sources, Summerboard, and Customize...Not sure if I needed to have all of those. But I was hoping someone could help me out and tell me how to get this theme now onto the ipod.
Thanks so much!