Several of us have been out there. I even drove a whole group of us last time but can't remember the actual directions. I know it's NOT in JT Nat'l Park. If you PM BonoComet or BonoFox1; they might be able to help you out. It helps to take a photo of the site out there with you - I think that's what Comet did the first time, just lined up the horizon with the pics. I do know that it's about 1/4 mile off the highway so you can't really see it from the road w/o binoculars. And you should plan on going to Zabriskie Point too, where the actual cover of the JT album was shot. It's BEAUTIFUL!
And if you do go, I'll tell you what those before me told me, please be respectful of the tree and the site. Don't sit/stand/climb on what remains of it - you can see, it's already decomposing. Also, when we were there the 1st time, the park ranger came out and said we weren't supposed to be there, but since fans had always been very good about not leaving ANY trash or anything and being careful where they walked, etc, he'd sort of "let it slide". He was pretty clear that he didn't want directions / coordinates posted on the internet though. He gave us one of these
asking how we found the place.
Also, just beyond the tree is Native American burial ground (or sacred ground of some kind) so, you know, just be careful and respectful.
Good luck!