Most organizations upgrade their operating systems every few years. A lot of these organizations have skipped the Windows Vista operating system. They are now preparing to go directly to Windows 7. There is not any simple options for a Windows XP to Windows 7 migration.
Users do not like change in general. So it is best to let the users know why you are upgrading their operating systems. Involve them early in the requirements gathering stage. You should set aside a lot of time for migrating data to new application as well.
Set a firm deadline when you require users to be off of Windows XP. Know that any legacy applications will also take a while to migrate. It would be good to have a date when the legacy applications are frozen and get no more upgrades.
You had better be prepared to deal with the legacy app situation. Know the full costs of their maintenance well in advance of the move to Windows 7. Know this. In the end, you will exert a lot of energy but get no thanks for your Windows platform upgrade.