Wait what? You guys haven't played as Luigi in Super Mario 64 yet? It's really easy. The 2041 thing is a code. It goes 2-0 and 4-1. 2-0=2. B is the 2nd letter in the alphabet. 4-1=3, and C is the 3rd letter in the alphabet. Starting to make sense?
What you have to do is go next to Yoshi and press the B button as well as all the C buttons simultaneously 2,041 times. You might need a friend to help reach all those C buttons. Don't worry about counting, just keeping mashing them simultaneously until Mario jumps on Yoshi.
This next part is really cool. I'm still surprised more people don't know about this though, I thought there was a big news story on IGN and stuff a few years back... that's how I heard about it at least...
Anyway, you have control of Mario riding Yoshi! It doesn't work that well (you can't enter doors or use any of his special abilities) but it's still pretty cool. What you do now is take Yoshi and jump behind the waterfall, obviously this is only possible while riding Yoshi. You'll find a little cave area, and standing in the middle is Luigi! Just run over to him on Yoshi and he'll say something like "Hey Mario, is it my turn finally?" Tell him Yes and the camera will switch to Luigi, leaving Mario and Yoshi in the cave. You can now play around in all the worlds as Luigi, though sadly you can't save having switched over. I'm also pretty sure there's no way to switch back to Mario while playing, other than restarting the game.
Luigi plays just like Mario, but still, it's pretty awesome after all these years to see a green-suited Mario Bro. wreaking havoc in 64-bit glory!
