For those who are interested in starting Ashtanga Vinyasa Yoga here is a clip of Maria Villella, a yoga teacher in America, demostrating Surya Namaskara A and B from Ashtanga Vinyasa yoga system.
Ashtanga Vinyasa yoga is a sequence of asanas starting with Surya Namaskara A and B to warm up. The series then goes into a standing asana sequence, a sitting asana sequence and then a finishing sequence. Beginners to this method start with the primary series of postures, which helps you prepare by building strength and flexibility for the advance series and asanas later on in the practice. Each asana is held for a number of counts and a vinyasa flow is performed in between each asana.
I have only just started to practice Ashtanga method, however I find that it is a strong and challenging practice. I also find having a defined set sequence and the counting in each asana meditative and calming.
Yoga journal also have a video showing a modified beginner variation too..
Surya Namaskara Variation, Yoga Journal