I am supposed to use the name and password of my account on these message boards...right?
Not at all... there are three different types of "registration" that are not rarely confused:
(1) Your mIRC board registration
, which enables you to post your comments in the mIRC Message Board;
(2) Your mIRC registration
, which proves that you have paid for mIRC, and which enables you to remove the shareware notice when you run the program; and,
(3) Your registration to a nickname in a particular network (e.g., Undernet, Dalnet, Efnet, etc), which is unique
to each network. That enables you (among other things) to join certain chatrooms that have been set to +r. For further help on how to register your nickname, you should join the network's #help channel, since, as stated above, each network may (or not) have it's own way of registering/identifying to a nick.
Sometimes if you type /nickserv identify help or /authserv help you'll get some help with registering/identifying as well.
There are not few threads that have dealt with these differences and explain how to register for each case.
Hope it helps