This kind of effort is like any other major project. Figure out what you want to do, how you're going to pull it off, then go do it.
1: Define your requirements, constraints and budget
2: Pick your technology (VPN, Frame Relay, ATM, etc)
3: Build a RFP, distribute to vendors, review their responses and pick one
4: Finalize your plan, get your facilities in orer
5: Order the circuits and get the connectivity provisioned
6: Test the heck out of it.
7: CAREFULLY cut traffic to it.
8: Pray
- G