I don't think I have heard of an FTP client for C128 or C64. I think the most useful thing I have heard of is to run a file server on the C128 to transfer stuff from a PC. There should be a game or two that supports network as well I think.
Ive got one of these adapters on the way but I am not sure what all it can do. I bought it for use on BBS's but as I wait for it I am wondering what else you guys have been able to do with it.
For instance can I ftp with it?
I am not aware of any "tcp" stack for C-64 (maybe Contiki?) that would let you do ftp. I have an SD card adapter for my c-128, so I just typically download stuff my PC to my sdcard, and then plop it into the c-128's sd card reader. Heck with the FTP
With the network card, you can however atdt telnet to bbs and use zmodem protocol to download files and stuff. It is fun. You may be able to run you own bbs over the internet.