I'm a bit confused...

Can you verify my understanding of your problem...

1. You are physically connected directly to your UNIX
machine via a cable attached to your PC's serial port.
I assume you have a NULL Modem attached?

2. You are NOT using TCP/IP (dialing out to the Internet
via a modem).

3. You can no longer connect to your PC's COM port
using Hyper-Terminal.

Please let me know if these assumptions are correct
before we proceed further.