WinUAE has a TCP/IP stack built in. If you enable bsdsocket.library emulation (which is default in AF5 IIRC), you don't need a sperate stack, WinUAE uses the Windows' one.
If you can use FTP, you can use any other protocol, too, where is the problem ? Just get a web browser, an e-mail program, an IRC client, everything you want. Search Aminet's comm directory.
http://us.aminet.net