I am an attorney in St. Louis, Missouri, and I handle DWI cases. You can email me at St.LouisAttorney@sbcglobal.net to discuss your case. Depending on where in Missouri you got the DWI, I can either handle it for you, or refer you to someone who can. My fees are very reasonable, and you can ignore the vast majority of other responses to this question -- they have no idea what they're talking about.
Basically, if it's your first DWI and the rest of your record is OK, we'll most likely get you what's called a Suspended Imposition of Sentence, and place you on probation for a year or two. If you don't get into any trouble during that time, the DWI never shows on your criminal record - it just disappears. As a condition of probation, you'll probably have to do some community service, and you'll have to take a class called Substance Abuse Traffic Offender Program (SATOP) which is a class on why you shouldn't drink and drive. You'll have to pay a small fine, and that's about it. As for keeping your license, you'll most likely lose it for 90 days. During the first 30 of those, you can't drive at all, but you can get a Hardship License for the last 60 of those 90 days, to drive to necessary places, like to work or a doctor's office.
By the way, feel free to pick my answer as the best one. : )
The prosecuting attorney represents the State (or Crown, you didn't say where you are) in criminal prosecutions.
Any licensed lawyer can be a prosecutor. So - in the US - 4 years of college plus three years of Law School.