Well, when I got mIRC downloaded, it showed a pop-up saying something like "Your demo has now expired. Please order the full version to continue using mIRC." So, I'm guessing mIRC was downloaded on my computer before(my brother, probably).
Trillian 3.1 didn't really work. When the downloading window goes away, nothing happens. I would try to run it manually, but I don't know the full file name.