Be very cautious.
Going vegetarian is a challenging food lifestyle choice in itself. In order to ensure you're still receiving enough protein and enough of things like iron that meat provides the rest of us, you need to be very careful about your diet and very exacting on what you eat and how much.
The 17 day diet is not a vegetarian based diet, and may not be able to be simply done by subbing the meat. You are extremely likely to be very low on many vitamins and minerals if you did this.
You would be better off to focus on your vegetarian choices and how you can eat healthily maintaining that lifestyle, and if you feel you need a "kick start" just ensure you get plenty of fibre and water and absolutely no junk food for two weeks. That should be more than enough of a "kick" to get you going.