Hello. In my experience, backbending, twisting and inversions help ibs-c the most. Also, I think if you can't find a teacher, books are a bigger help than videos since you can take your time reading the details and going into and out of the postures at your own pace. The problem with videos is you have to crane your neck to look at the tv, which puts it out of alignment with your spine and both endangers you and compromises the pose.
Yoga Journal (http://yogajournal.com/poses/index.cfm?ctsrc=tnav) has detailed explanations of many postures, and is a great way to get started. (the poses are listed in both the english and sanskrit names so they're easier to find)
Some of the best beginner poses for ibs-c are: downward facing dog childs pose cobra pose supported shoulderstand (be careful especially of your low back and neck with this one) plank pose and side plank pose (if you pull your belly in firmly and keep your spine aligned) finish with corpse pose
Start by holding each pose for 5-10 slow breaths, and try not to do them right after eating.
Also, heather has a list of good yoga poses somewhere on this site. You might want to try them out. If you have any questions feel free to ask. I still have several months before I complete my yoga teacher training, but I have been practicing for almost ten years, and I'd be happy to help you (or anyone) develop a home practice if you give me more information about yourself. Just send me a message.
Yoga has helped me a lot, and I want to share the benefits.