Okay,
I cannot provide much help with Mac OSX, but it's pretty simple. First, in the server-manager GUI, make sure you have "Remote Access" set to allow FTP. Then make sure you are in a group that has access to the ibay you want to work in.
Finally, FTP with your username and password. This takes you to you user's $HOME directory. So, you'll need to find the ibays. They are located in :
/ibays/<ibayname>/
Basically, go back to the root and then work up through ibays and the ibayname.