If you can, try to get some advice from a nutritionist/dietician familiar with vegan nutrition. I'm gluten free, and even that has some nutritional consequences that I have to stay aware of, but vegans face some serious challenges to stave off nutrient deficiencies. Vegetarians, generally defined as people who don't eat meat, but do consume dairy/eggs, have an easier road than vegans nutritionally.
From what I understand, it can be done, but it takes some work and dedication. Probably much like my gf transition, the hard part was making the change in the first place -- now it's all habit. Once you know what you need to do, and get used to doing it, it will seem as normal to you as your previous diet once did.
Starting Weight: 260 lbs. (November 2010)
Quasi-Maintenance: 165 lbs. (June 2011)
Goal Weight: 150 lbs. (reached December 8, 2011)
Size 22W to Size 4
Currently maintaining within 5 lbs. (+ or -) of goal. I weigh daily, but also use a tape measure and the fit of my clothes to guage how well I'm doing.