Best way to inform employer about DUI in job interview.?

Right now I work at a non profit association...have been for a few years. I sent my resume for this new job in another association. A few days ago I had my phone interview...the HR woman loved me..said I had the best resume, etc. I also have great references from high level bosses, etc. I have my face to face interview on Monday morning. One problem...I made a dumb mistake a few months back and got a DUI. Decided to drive home from my brothers after drinking cause it was only a half mile away..assumed it was ok but as soon as I pulled out of the driveway...cop was there..DUI end of story. Horrible mistake and I deserved it..bad judgement. Anyway, my question is how do I bring this up and when? It hasn't been asked..yet but I am assuming they will want me to consent to a background check every company does one pretty much? Should I just write it on the form or try and explain what happened and my remorse. I wouldn't lie on the app im sure that would disqualify me automatically. Its a tough situation because right now I am the lead candidate. Thanks in advance everyone.