I am a yoga teacher and thought I'd add a little guidance here. Generally, it's not really a good idea to learn yoga without a teacher - there's so much that you simply cannot learn from books and video's. However once you get started they are a good way to keep up the momentum of a home practice which is where, to be honest, you make all your "progress" in yoga anyway.
Yoga traditionally was taught one-to-one and it's only when it arrived here in the west that we created group classes. Some teachers are better than others, as with all occupations/vocations, so don't be afraid to check out different classes to find teachers (and classmates) who you "connect" with.
Alternately (and especially if your IBS is very limiting) you could find a teacher who is trained and experienced in ygoa therapy, who will help you develop an individualised problem that will go a long way to helping you manage IBS, if not actually help reduce or remove its symptoms and/or causes. In my opinion the best teachers in yoga therapy are those who follow the Krishnamacharya (Viniyoga) tradition.
There's a lot to be had from a good yoga practice for sufferers of IBS, however it's hard work at times and you will only get as much out of it as you put in. If you're not willing to put in the effort, obviously you don't really want the changes THAT badly.