I recommend starting with a shorter session, 20 or 30 minutes, and watching it first so you know what the instructor is going to do. Sun Salutations are fairly standard in most forms of yoga and yoga practices, so it's a good idea to know how to do those.Any tips on how to follow a DVD when you're laying on a yoga mat and can't quite see the tv without stopping what you're trying to do.
In fact, if I don't have time for a full yoga practice I do 5 or 10 of these as they stretch and strengthen your whole body.
It takes a long time to get your movements in synch with your breathing and to be able to get into a pose as well as an instructor on a video, but don't let that put you off. You'll be getting all the benefits of the pose from practicing at the level your body is at right now.
The breathing is the important part. Don't worry about making the pose look like it does on the video. Focus on taking deep breaths and modify the poses so they're comfortable for you.
The idea is to make the poses fit your body, not make your body fit into the pose.
I did a 45 minute cardio flow today. I needed something to warm me up.