[BGL] How to change the type of vertex_descriptor??

Hi, I have a BGL graph in the following manner: typedef adjacency_list < vecS, vecS, directedS, no_property, property > > Graph; I also have: typedef graph_traits<Graph>::vertex_descriptor Vertex; Now, the default vertex_descriptor seems to be unsigned int. How do I change this to int? Also, where (in which file) is the default set? On another note: the online reference manual is pretty good in my opinion, but it's hard to get a real overview of the contents. It also lacks an index, making it hard to look up questions like the one above. Is the book any better in this respect? Any other references worth looking up - books or webpages? Thanks, Erik