The last few weeks have seen an increase in violence in Somalia. Insurgents have stepped up attacks on the Ethiopian army and on the Somali transitional government it's backing. Ethiopia sent it's troops into Somalia at the end of 2006, to remove an Islamist movement - the Islamic Courts - from the capital. But now Ethiopia is bogged down and anger at its presence has boosted supported for the insurgents. In Assignment, Rob Walker goes in search of a radical Islamist movement which is playing an increasingly deadly role in the conflict.