ahhh mIRC, my oldest form of obtaining any media.
I've used hotline, kazaa, bittorrent, and other file sharing programs of the sort, but my heart still stays with IRC. I resort to the other programs if all else fails in IRC.
First, you have to be on the right server. Most efnet servers have channels where people are file sharing.
There's some commands to be familiar with, and there's conditions on rooms that you need to work around. If everyone's chatting and what not, you can do a !list to have all the bots in the room flood out their trigger commands. Trigger commands are set by the bot's owner and trigger the chat session between you and the bot (fileshare).
There's also rooms where the only ones that can say anything to the channel are bots. Usually these list off the goodies they have and there's no need to establish a chat connection. These are usually named with numbers and the characters: "x" "d and/or "c" in them. If you double click on these and send a private message to them of: "/xdcc list", some may list their contents to the room... its like a trigger/on-demand type of thing. Otherwise, you just wait.
Once you do find something that interests you, there's two ways to download it. If you're in a chat session with a bot, you'll need to do: "get (filename.ext)". If you're in the main channel and the bot is listing its goodies there, there's usually a packet # associated with the file. You simply remember the number, give a message to the bot and do: "/xdcc send #x".
But yea, there's a LOT more user friendly programs out there for filesharing. Searching for one specific thing on IRC is no good. I mainly go on there when I'm bored, have free space, and nothing else better to do with my time.