The design methodology is broken down into three (or four) phases:
First is the architectural vision. During this phase you will define the scope, assign goals, list requirements, state assumptions, define constraints and outline the risks. This phase will server a the roadmap for the remainder of the project.
The next phase is the architectural analysis, which we actually take a more in-depth view of the existing infrastructure. Gather and analyze information on existing network, servers and storage. Documenting detailed information on all these pieces is key because this information will be needed later on.
The third phase is the technology architecture, where we take all the information from the previous phase and use it to create a conceptual design, a logical design and a physical design.
There can be a migration planning phase as a fourth phase, but I usually like to think of this as a separate project. With this phase, the information gathered in phase is valuable for their migration from physical to virtual. This information should include the processor, memory and disk utilizations.