In this paper, we propose a network-aware multicast scheme to supply instantaneous VOD (video-on-demand) services. Being different from traditional VOD systems, this system is implemented based on peer-to-peer grid. By taking advantage of the large storage and the powerful processing capability in client-side devices, the user host serves as both a client and a non-dedicated video server. The system capability is enhanced due to the contribution of user hosts. Peer groups are formed as a collection of peers that share similar interest, and workload may be fairly apportioned among autonomous groups. In this VOD system, the adaptive video delivery mainly employs a new dynamic buffering algorithm and an improved video multicast strategy to achieve an optimal utilization of system resources, and the network-aware adaptation makes the system more robust. In cooperating with each other, the relevant servers can supply instantaneous video services for local users.