Hello, Notfish;
One thing I always check out whenever I have trouble with serial comms : do I have control of the COM port? Since I run both Siemens and Rockwell software on the same computer, I always have to make sure RsLinx is shutdown (manually) before I connect from my Siemens software; RsLinx is a communications predator, it locks up the COM port. This might not be the exact scenario you are running, but another program could be hampering communications on the COM port of your computer.
Cheapest way I found to test the COM port is to setup a serial mouse on it and check whether the system detects it (this involves more work on a Win NT4.0 system, but it is fast on W2K or XP).
At least this way you eliminate one possible gridlock point. Try it and come back to us; we'll see about more solutions if this does not solve the problem.
Hope this helps,
Daniel Chartier