bah: led zepplin might be some of the best rock, but that solo in heartbreaker is not that hard. he plays the diatonic harmonic minor scale (i think, gotta listen to it again) up and down about 3 times, then he does a series of pulls offs and hammer ons just like in the end of the solo to stairway cept faster. Just does some standard shredding. but if shredding is what your into, cool go for it.
You want a good/relatively hard solo? try the solo in steely dan - kid charlamange or even better yet the intro in john mayer - man on the side, dont even say anything until you try it with an acoustic, sooo incredbily hard with an acoustic guitar. They have awsome rhythm and speed. Just figured out the one in man on the side today (took probably about 6 hrs total of playing), but i still need to get the last rift down really solid, he goes with so freakin impossibly quick speed on a acoustic. Sigh, when will i ever be that good?
edit: to tune dadddd, what you do is get the guitar in standard tuning (with a pitch fork or tuner), tune the 6 string down until its in tune with the open 4. Then tune the open 1 string to either the open 6 or the open 4. Do bascially the same for the 3,2 string. Oh ya you gotta have like high gauge string on the B and G string if you are gonna do this tuning because your tuning the B string down 9 notes, and the G string six, which basically makes your string loose almost all tension, so what happens is that if you even just barely barely, ever so slightly (espeically the B string) bend the string up or to the side, the chord will sound aweful because it will be out of tune. I wouldn't do a DADDD tune unless the song specifically calls for it, just learn the chords.