The first step to get ready to migrate to Windows 7 is to understand your environment very well. You will probably want to start identifying your applications and hardware. It is also a good time to consider improving some of your internal procedures such as OS deployment and application distribution, as well as improvements on user experience.
You should start with a hardware and software inventory. I recommend using MAP, the Microsoft Assessment and Planning Toolkit. MAP is an agentless application that will take an inventory of machines on your network and tell you what hardware they have. It will also tell you what software is installed on the machines. It will go even further and tell you if the machines are ready to run Windows 7 and Office 2010, based on a few pre-defined factors. Make sure you take out DVD Drive as a requirement (this is a default value), as you will probably use something like WDS and/or MDT to deploy Windows 7. MAP can do much more; check the resources at the end of this article.
MAP will provide the inventory, but it is still hard to understand how the applications are being used. Having an application installed does not mean that the users actually use it. Furthermore, do they use the application when they are at the office or when they work from home? How many concurrent users do you have for an application? Those answers can seriously affect the price you will pay for your licences. To tackle this problem I recommend Centrix WorkSpace iQ. It will monitor application usage on workstation with the agent installed. It can also help you understand how laptops are used. I had a client to run the laptop analysis in 700 laptops and after 3 months we found out that only 96 of them where ever taken away from the docking station, which means that potentially 604 of them can be replaced by a desktop on the next hardware refresh cycle.
Once you understand your hardware and software current state you will need to rationalize the software that is used on your company. It is a great time to remove old versions and retire legacy software. On average each retired application can save up to 3000 dollars during a migration. Choose carefully with software will be delivered on your new Windows platform and work to solve potential application compatibility issues.
Make a list of the hardware that needs to be replaced and find a solution for it, If you have the budget get new machines. If you are tight in budget but have a decent licence agreement give Windows ThinPC a try.