Peer-to-peer systems and applications are distributed systems without any centralized control. The core operation in most peer-to-peer systems is efficient location of data items. The current well-known peer-to-peer systems like Napster and Gnutella have scalability problem in location of data items. To solve the scalability problem, some scalable peer-to-peer lookup services show up, such as CAN, Chord, Pastry, and Tapestry. In this paper, we propose a self organizing hierarchical virtual network infrastructure, called Grapes, for peer-to-peer lookup services. Hierarchical approach of Grapes brings two benefits. First, a node can find data in its sub-network with the high probability due to the data replication in its sub-network. Second, the hierarchical structure makes lookup hops shorter than those of the flat one.