The tune is I'm Freaking Out, written by Steve Morse and played by the Dixie Dregs on their LP Dregs of the Earth. Andy West on bass.
This sucker had me stumped for years and I had forgotten about it but I came across it the other day and, with the wonder of Transcription software, I was able to transcribe the main theme. It's an absolute nightmare to play at tempo (only about 134 bpm but it's all 16th notes) and is played by Andy West with a pick (on an Alembic, IIRC). The part transcribed appears at 2.21 on this Youtube video and repeats several times throughout.
http://www.youtube.com/watch?v=hDC43Tm3RQ8