You should already be applying if you want to get in for Fall 2007. The application opened on May 15th, and people have been submitting since. If you were to have you're transcripts sent to AADSAS today and submitted a complete application to AADSAS today, it would still take a few weeks for them to recieve the transcripts and verify the GPA (around August 5th lets say)
Then, you'd have to wait 4-8 weeks while AADSAS sits on your application before they mail it...around September 21st let's say. Hopefully your letters of rec would be done by then also.
Late september is starting to get into that shady area of applying. It's not LATE...but it's no longer EARLY
You want to take the DAT whenever you are ready cause it isn't easy. But most people are trying to take it now or before their application gets to schools. (this august for most people). However, if you do apply right now and have to wait for AADSAS to verify your grades and send your file to the dental schools, then you could wait until early september to take the DAT since no school would have your file before then anyway and it only takes about a week for your DAT scores to go from the ADA to the Schools.