The problem with xmodem is that it rounds the file size up to a 128-byte multiple. This is OK to transfer text or a tar file--tar will ignore the trailing padding. If you transfer a compressed file, it fails because the uncompress fails.

zmodem (rzsz program) still appears to be available from the author at Omen Technology INC, but you'll have to compile it to get an AIX binary. Refer also to 4.28: Zmodem - File transfer.

Another technique is to use serial line internet protocol (SLIP). AIX can do TCP/IP over a TTY port. Login (getty) should not be active on the port. Use a port other than S1 (the console port) because you don't want to mess up the console port (unless you also have a graphics adapter for a console). Configure each end with a private IP address (e.g., 10.0.0.1 and 10.0.0.2) Then you can use ftp for file transfers. You can also have multiple telnet sessions, which is nice. X-windows even works; although it is slow to open a window, performance is OK after that. Refer to

Serial Line Internet Protocol

Refer to http://www.sics.se/~bg/telos/slipintro.pdf for info on configuring SLIP on Windows.

One more even simpler solution might be to use SLiRP, which is available here: http://slirp.sourceforge.net/ and documented here: http://sunsite.nus.edu.sg/pub/slirp/. You still have to configure SLIP on the Windows side.

I used to use SLiRP to access the Internet when I only had a dial-up shell account on a remote UNIX host. I also used it to access a local RS/6000 from a PC when I did not have an Ethernet card in the PC.