Hi,
Google for serial port sniffer and you should find plenty of programs. Another REALLY handy tool is logic analyzer with protocol decoding. I've got a Saleae LOGIC and it's just a great little tool to use for things like this as it lets you see what is ACTUALLY going down the wires.

Since you have another thread on a similar subject open I suspect the two to be about the same problem. The serial communicator in MCS works just fine, but it can only display ASCII data. If your device isn't sending pure ASCII data then it won't display it properly which MIGHT be why you see the byte count going up but no data being displayed. Then, of course, if the polarity is wrong - as Robert mentioned in the other thread, it won't work either.

In the code you posted you have the mode (the polarity) set differently for DEBUG vs DEBUGIN.

/Henrik.