rotate to object

[jargon]

I vaguely remember there's a method to rotate one object to another object but I didn't want to look through all my old files trying to see how it's done (I know one can do it in Vizard though). Specifically I have a triangle object and I have another identical triangle object but rotated to some other. How does one rotate the one object to the other? Furthermore, Can you do it without converting it to quaternions (like is there a rotate object to object command?)
thanks,
jargon