legend titles?

[El Jeffo]

say I do 
plot(t, x1, t, x2, t, x3)
I get like in the upper right hand corner:
line 1 -----
line 2 -----

how do I change those captions (line x) to the equation... I don't need it
too magical... perhaps I have to type it manually, and that's fine... just
couldn't find the right variable, function to call or plot() option.

Also is it possible to place arbitrary text into the window?  hehe, yeah
ask for the world why don't I, go ahead and tell me to plot a matrix of
points...

Thanks

Jeff