Trying to get PowerChute to "see" APC UPS unit

I'm trying to install the APC Powerchute Client software on our server (PowerEdge 2900, Windows Server 2003 R2), which is connected to an APC Smart-UPS 750 via serial cable.  The cable is connected to the COM1 port of the server; the server has only one serial port. If I run the Powerchute installer with the "autodetect port settings" option, it will stall out during the port scan until I kill it from Task Manager--I've let it run overnight and it has never gone beyond the detecting port settings screen.  If I manually specify the port during the install, the client can't talk to the UPS after the install is complete. Is there something I need to do differently during the install, or can the Powerchute client just not communicate to the UPS over a serial cable?