I got my old Linux tablet working again and connected to the Reprap. Guess what I discovered? The damn thing can't connect. This indicated that the problem had nothing to do with my Windows workstation at all and was probably hardware related. I pulled out the 6 conductor cable between the main board and the USB/TTY adapter and, sure enough, one of the leads was dead between the two connectors. I made up a new cable and "voila" both Pronterface and Repsnapper can now connect with no problems.
I have the X and Y axis moving fine but my Z axis won't move anymore. Probably more of my sloppy wiring. The hot end is heating up but I don't seem to be getting any temp readings back from the thermistor. Again, probably a hardware problem.
I tried to sending a command to the extruder but the motor didn't do anything. I only thought afterward that the software may prevent it from running until the hot end reaches operating temperature to prevent damage from trying to push un-melted filament through the tip. I will check the code for this.
So it looks like I am finally able to proceed with final debugging and getting Mendel working. There's a lesson to be learned here - don't assume anything. Just because things were working on the Linux tablet didn't automatically rule out hardware problems being the culprit. It was really my tunnel vision on the ports that kept me from examining other possible issues earlier.
Oh well, Onward to Victory!!