Well, it appears I have finally solved the problems.
After buying yet another new motherboard last night, I was finally able to get my computer to boot. It turns out that the Asus A7N8X I bought was defective, so it is being returned. Also, the XP1600+ I bought (OEM) was defective as well.
I now have a new Gigabyte GA-7VA KT400 -based board with an Athlon XP2000+. One of my sticks of PC2100 is bad, and the other seems to work ok. Something bad happened to my setup, which I'm attributing to my old motherboard. It seems that it managed to torch my CPU, and memory, and itself. I don't know the root cause of it, but as of now things seem to be back in order. In the near future, I'm going to have to pick up some PC2700 or PC3200 depending on budget constraints in the new year.
All that being said, I'm glad to finally get my machine back up and running, and can't wait to get in the skies again. Downloaded the new 1.11 patch 1 version last night and played a bit offline. It looks pretty sweet...
See you all in the skies, and thanks for all the input you've given in this thread.
Semper Fi.