Apparently, LZ had a little help from an unknown band from the 60's called "Spirit".

At first, LZ said they didn't know Spirit's music.  However, they toured with Spirit in the late 60's.  Furthermore, Spirit's song "Taurus" was released in '68.  "Stairway" came out in '71.

I'm not really a big LZ fan, but I'm a little bummed that the luster on one of the most iconic guitar intros is a bit tarnished. :(

You can compare the songs here: