Making decision for a new IT application.

For this discussion imagine that you are a manager at an organization similar to the company in the insurance case and you have to make a buy decision for a new IT application.
As in the case, the employees who are going to be using the system are resistant to the change -- and may fight you on it.
At the same time, the vendor options keep shifting as illustrated in the dentist office reading.
How do you manage this? How do you get buy-in from your employees and at the same time pick a vendor who you can rely on?

Sample Solution