if you can't find CyberDuck, there are other programs you can try...for now i'll post a walkthrough for Cyberduck
Once you have the program up and running, click the 'Open Connection' button. You should get a new window drop down asking for some info.
for protocol, select 'SFTP (SSH Secure blah blah blah)'
for Server, you need to type your iPhone/iPoT IP address...you can find this by going into your system settings (on your iPhone), Wifi settings, and hitting the blue arrow next to your connection
for UserName, type in 'root' (no speech marks)
for Password, type in 'alpine' (no speech marks)
Leave all the other info as it is, and click connect
you should now have access to your iphone, and should see a pair of folders

well done, your looking at the files on your iphone
you then need to navigate to
/private/var/mobile/library/summerboard/themes if your new themes arent there, you need to put them there
Installer will automatically download any new themes you choose to
/private/var/root/library/summerboard/themes. You'll have to cut them from this directory and paste them into the correct directory
(green = the right directory, red is the wrong one

)