Steve,

I have the tab for this and all other Robert Johnson tunes in a book by Scott Ainslie and Dave Whitehill. Here's the book info:
Scott Ainslie and Dave Whitehill, "Robert Johnson: At The Crossroads - The Authoritative Guitar Transcriptions", Hal Leonard Publishing, 1992.
The book is pretty good and has some interesting historical notes. If you're a Robert Johnson fan you might want to have a look at it.
If I get a chance and no one beats me to it, I'll transcribe the tab to ASCII Text and post it. Johnson plays this song in Open E (EBEG#Be). I play in Open D (DADF#Ad) because it suits my vocal range and it's easier to switch tunings from open D to DADGAD if I feel like it.
Dave T