No offense intended but you do realise mirc is a chat application right? If you want to run a bot that has to connect to hundreds of channels, you really need to look at other methods, like C, C++, Perl, python, and of course eggdrop/windrop if you insist running windows. Also what irc network allows a user to join all those channels?
However if you really insist on using mirc/windows for this folly then look at spending some money and upgrade your memory/cpu or whole system.
Best of luck
