Although Grid computing has become popular in scientific research and the enterprise domain, there is no way a personal user who does not belong to any organization can construct or access the Grid system for solving her problems. The main goal of this paper is to propose a lightweight Personal Grid that is self-organized without complicated configuration and infrastructural support like central servers and self-managed with the cooperation of participants. The key component of our system is the supernode network designed for autonomously and efficiently constructing the Grid system. Based on the supernode network, our Personal Grid system forms a virtual organization (VO) with nodes having physical proximity. Therefore, communication latency between nodes in a VO can be minimized. Moreover, hierarchical scheduling is adopted using the two-level structure of the supernode network and new service architecture is proposed to improve the reusability of applications.