I recently came across this excellent tool called Windows Vista ROI Calculator.
This tool developed independently by leading IT analyst firm IDC and ROI/TCO experts at Alinean Inc., helps companies determine the potential benefits and return on investment from implementing Windows Vista Business or Windows Vista Enterprise. By providing a few key data points about the organisation, this tool can be used to create a preliminary business case for migrating to Windows Vista.
The screenshots shown are for default assumptions.
First you have to fill up the Questionnaire giving details of current OS profile, Vista versions planning to buy, percentage of PC to be migrated etc. Here one can also take help of Windows Vista Hardware assessment tool provided by Microsoft as a link is provided in the page itself.
(MS Application Compatibility toolkit link could also have been provided with this)
After filling all the details, one gets the Benefits summary table or Benefits summary chart.Next we get the investment summary table or chart.And lastly ROI Analysis summary Table or Chart is provided.
The complete thing can be saved as a report in .pdf format.