What you say about the CM11A having trouble with the serial port is true. As beta tester for both that and the CM14A, the serial port was a significant issue. But, just because X10 can't learn how to use a serial port properly doesn't mean that other manufacturers have the same problem. Back at the lab I developed many systems that worked just fine through the serial port using default Windows drivers. As I recall, X10 rolled their own for the CM11A and CM14A.
The Ocelot has never had any problem communicating through the serial ports in any of my computers - from W95 through XP SP2. I use multiple serial ports to access a number of devices, ranging from the Carrier/Bryant HVAC system monitor to the Rain8 irrigation controller. No problems with any of them.
If you want fancy graphics and relatively simple X10 control, go for the CM15A. If you really want to automate your house, the Ocelot is a good entry level system. Since the original poster apparently already has one, it might be worth reading the manual. That and the CMAX program are available for download at:
http://www.appdig.com/adicon_new/download.htmJeff