I found a good article by John McRae on deploying Compute Cluster with Windows Deployment Service here.
Although we shipped WDS in Windows Server 2003 SP2 and we use in compute cluster pack SP1, we use it in legacy (RIS) mode. This article describes how to exploit full WDS for deployment. Image and multicast-based deployment (available in WDS) are fundamental for large clusters. They use network bandwidth efficiently, hence they allow simultaneous deployment of 100+ nodes. RIS practical limit over Gigabit Ethernet is about 20 (again, this is a rule of thumb, not scientific measurement).