VegNews does an issue on vegan weddings every year. I'm sure you can get backorders online or find some old copies at a library. Here's a link to the 2009 article: http://vegnews.com/articles/page.do?pageId=528&catId=7
When I got married it wasn't much of a problem to find a dress made from plants or synthetics. Fewer than 50% of the dresses I liked were vegan, but that didn't make it too terrible. I just had to look at a lot of dresses. I shopped at about 5 different stores and narrowed it down to the ones I liked and then chose from there. For the dress, the issues were more about cost and fit
I actually still regret going to a specialized wedding dress boutique and wished I had gone for the cheaper ivory dress I found at a department store. It actually looked and fit better!
About the food: try finding a caterer who is willing to experiment. And then work with him/her to develop a vegan menu. Provide recipes and ideas. It will require you to work harder than if you had a vegan caterer but in the long run it's worth it.
Same goes for cake. Just call around and ask. You may be surprised to learn that so-and-so baker who usually puts eggs in everything has a daughter or nephew who is allegic to eggs. Someone like that is far more willing to learn how to accomodate a vegan than the average baker. So go out on a limb and just ask everyone a lot of questions to see if anyone is motivated to help you.For family who disagree with a vegan wedding, just remind them that this is your celebration and having nonvegan food makes you very sad. It's supposed to be your big happy day and they want something that will make you terribly sad.
Pull a guilt-trip. If ever there is a good time to do that, now is the time. You are the bride and you get to be happy on your wedding day, period.
Remind them that it's just one meal and everyone can handle eating a vegan meal once in their lifetime. If you choose to compromise about it then change the time (people are more willing to not eat dead animals earlier in the day) or change the type of meal (for example, have cocktails and apps instead of a sit-down dinner). I had 80 people at my wedding reception and only 1 person complained that there wasn't any meat. Just one. And that wasn't because the other 79 were vegetarian, no, only a handful of people were already veg. Seriously, people can deal with whatever food you offer. It's not as big of a deal as any of your family members act like it is.