You can represent yourself -- although it is not a good idea. "Drunk driving" is a very complex field with increasingly harsh consequences. There is a minefield of complicated procedural, evidentiary, constitutional, sentencing and administrative license issues.

What can a lawyer do? Nothing (or worse) if he is not qualified in this highly specialized field -- no more than a family doctor could help with brain surgery. A qualified attorney, however, can review the case for defects, suppress evidence, compel discovery of such things as calibration and maintenance records for the breath machine, have blood samples independently analyzed, negotiate for a lesser charge or reduced sentence, obtain expert witnesses for trial, contest the administrative license suspension, etc.