I thought I would post this link as it is a good starting point for understanding how game engines work, and for the experienced coder this coupled with RakNet could make a decent base for an MMORPG. AFAIK this game engine is written in C++ and is open source. Hope this help's some of you get started in developing games.
Thanks for providing the linkage! In the very near future I'll be getting a thread/sticky up hopefully develop a listing of 2D/3D game engines, as well as game creator programs. I'll be sure to add this one to the listing.