What’s a good resource for using TCP/UDP? And which one is better for an MMORPG?
The Networking forum has a lot of discussions that will probably show you what you are looking for.
For the UDP vs TCP debate the is “The Thread” ( sticky thread at the top of that forum ) in which the topic was discussed, sometimes pasionately, to great extent. It really boils down to how you plan to implement your game and you’ll understand some of those issues reading the existing threads.
A new option for you now if you are really doing an MMORPG would be to check out Dark Star ( also has a forum ).
Good luck. MMORPGs are many levels of complexity higher than most other games indies put together. Hopefully you have started small and made a few basic single-player and two-player games that use the same technologies you plan to use for your MMORPG so you have all those kinks worked out.