The linked snippet is for checking online status via web portals for both messengers.
The problem is IRC and Yahoo are two distinctively different protocols and the only way of making them work together is using an interpreter between the two. The easiest way seems to be using IRC as the dominate protocol, and translating Yahoo into IRC language. I haven't seen someone actually do it for Yahoo yet, however there are Yahoo protocol handlers that provide the necessary functions to do such a project. Unfortunately I doubt they're up-to-date nor can I find them myself.
A great request would be to have someone interface the open source Purple (Prpl of the Pidgin/Gaim project) library into a mIRC DLL, as it's an excellent multi-protocol library that is up-to-date.
