All courses taken in college need to be entered regardless of whether or not there was a grade.
For detail questions like yours, it would be a better idea to check the AMCAS 2011 instructions before asking other 'just as experienced' pre-med students; plus, little things change from year to year, so answers to detail questions about this year's application could be different than last year's. http://www.aamc.org/students/amcas/2011amcasinstructions.pdf
Page 9 for starters, just search the file for 'audit'.
-admissions committee interviewer / senior medical student (14 days left)